right hemisphere essay

July 1, 2009

16 min read

Evolutionary Origins of Your Right and Left Brain

The division of labor by the two cerebral hemispheres—once thought to be uniquely human—predates us by half a billion years. Speech, right-handedness, facial recognition and the processing of spatial relations can be traced to brain asymmetries in early vertebrates

By Peter F. MacNeilage , Lesley J. Rogers & Giorgio Vallortigara

The left hemisphere of the human brain controls language, arguably our greatest mental attribute. It also controls the remarkable dexterity of the human right hand. The right hemisphere is dominant in the control of, among other things, our sense of how objects interrelate in space. Forty years ago the broad scientific consensus held that, in addition to language, right-handedness and the specialization of just one side of the brain for processing spatial relations occur in humans alone. Other animals, it was thought, have no hemispheric specializations of any kind.

Those beliefs fit well with the view that people have a special evolutionary status. Biologists and behavioral scientists generally agreed that right-handedness evolved in our hominid ancestors as they learned to build and use tools, about 2.5 million years ago. Right-handedness was also thought to underlie speech. Perhaps, as the story went, the left hemisphere simply added sign language to its repertoire of skilled manual actions and then converted it to speech. Or perhaps the left brain’s capacity for controlling manual action extended to controlling the vocal apparatus for speech. In either case, speech and language evolved from a relatively recent manual talent for toolmaking. The right hemisphere, meanwhile, was thought to have evolved by default into a center for processing spatial relations, after the left hemisphere became specialized for handedness.

In the past few decades, however, studies of many other animals have shown that their two brain hemispheres also have distinctive roles. Despite those findings, prevailing wisdom continues to hold that people are different. Many investigators still think the recently discovered specializations of the two brain hemispheres in nonhumans are unrelated to the human ones; the hemispheric specializations of humans began with humans.

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Here we present evidence for a radically different hypothesis that is gaining support, particularly among biologists. The specialization of each hemisphere in the human brain, we argue, was already present in its basic form when vertebrates emerged about 500 million years ago. We suggest that the more recent specializations of the brain hemispheres, including those of humans, evolved from the original ones by the Darwinian process of descent with modification. (In that process, capabilities relevant to ancient traits are changed or co-opted in the service of other developing traits.) Our hypothesis holds that the left hemisphere of the vertebrate brain was originally specialized for the control of well-established patterns of behavior under ordinary and familiar circumstances. In contrast, the right hemisphere, the primary seat of emotional arousal, was at first specialized for detecting and responding to unexpected stimuli in the environment.

In early vertebrates such a division of labor probably got its start when one or the other hemisphere developed a tendency to take control in particular circumstances. From that simple beginning, we propose, the right hemisphere took primary control in potentially dangerous circumstances that called for a rapid reaction from the animal—detecting a predator nearby, for instance. Otherwise, control passed to the left hemisphere. In other words, the left hemisphere became the seat of self-motivated behavior, sometimes called top-down control. (We stress that self-motivated behavior need not be innate; in fact, it is often learned.) The right hemisphere became the seat of environmentally motivated behavior, or bottom-up control. The processing that directs more specialized behaviors—language, toolmaking, spatial interrelations, facial recognition, and the like—evolved from those two basic controls.

The Left Hemisphere Most of the evidence that supports our hypothesis does not come from direct observation of the brain but rather from observations of behavior that favors one or the other side of the body. In the vertebrate nervous system the connections cross between body and brain—to a large degree, nerves to and from one side of the body are linked to the opposite-side hemisphere of the brain.

Evidence for the first part of our hypothesis—that the vertebrate left hemisphere specializes in controlling routine, internally directed behaviors—has been building for some time. One routine behavior with a rightward bias across many vertebrates is feeding. Fishes, reptiles and toads, for instance, tend to strike at prey on their right side under the guidance of their right eye and left hemisphere. In a variety of bird species—chickens, pigeons, quails and stilts—the right eye is the primary guide for various kinds of food pecking and prey capture. In one instance, such a lateralized feeding preference has apparently led to a lateralized bias in the animal’s external anatomy. The beak of the New Zealand wry-billed plover slopes to the right; that way, the plover’s right eye can guide the beak as the bird seeks food under small river stones.

As for mammals, the feeding behavior of humpback whales is a spectacular example of a lateral feeding preference. Phillip J. Clapham, now at the Alaska Fisheries Science Center in Seattle, and his colleagues discovered that 60 out of 75 whales had abrasions only on the right jaw; the other 15 whales had abrasions only on the left jaw. The findings were clear evidence that whales favor one side of the jaw for food gathering and that “right-jawedness” is by far the norm.

In short, in all vertebrate classes—fishes, reptiles, amphibians, birds and mammals—animals tend to retain what was probably an ancestral bias toward the use of the right side in the routine activity of feeding.

Origins of Right-Handedness What do these findings say about the alleged uniqueness of human right-handedness? Evidence for a right-side bias in birds and whales is intriguing, but it hardly makes a convincing argument against the old belief that right-handedness in humans had no evolutionary precursors. Yet more than a dozen recent studies have now demonstrated a right-handed bias among other primates, our closest evolutionary relatives—clearly suggesting that human right-handedness descended from that of earlier primates. The right-hand preference shows itself in monkeys (baboons, Cebus monkeys and rhesus macaques) as well as in apes, particularly in chimpanzees.

Many of the studies of apes have been done by William D. Hopkins of the Yerkes National Primate Research Center in Atlanta and his colleagues. Hopkins’s group observed right-hand preferences particularly in tasks that involved either coordinating both hands or reaching for food too high to grab without standing upright. For example, experimenters placed honey (a favorite food) inside a short length of plastic pipe and gave the pipe to one of the apes. To get the honey, the ape had to pick up the pipe in one hand and scrape out the honey with one finger of the opposite hand. By a ratio of 2 to 1, the apes preferred to scrape honey out with a finger of the right hand. Similarly, in the reaching experiments, the apes usually grabbed the food they wanted with the right hand.

The Yerkes findings also suggest to us that as early primates evolved to undertake harder and more elaborate tasks for finding food, their handedness preferences became stronger, too. The reason, we suspect, is that performing ever more complex tasks made it increasingly necessary for the control signals from the brain to pass as directly as possible to the more skilled hand. Since the most direct route from the left hemisphere—the hemisphere specialized for routine tasks—to the body follows the body-crossing pathways of the peripheral nerves, the right hand increasingly became the preferred hand among nonhuman primates for performing elaborate, albeit routine, tasks.

Communication and the Left Brain The evolutionary descent of human right-handed dexterity via the modification of ancient feeding behavior in ancestral higher primates now seems very likely. But could feeding behavior also have given rise to the left-brain specialization for language? Actually we do not mean to suggest that this development was direct. Rather we argue that the “language brain” emerged from an intermediate and somewhat less primitive specialization of the left hemisphere—namely, its specialization for routine communication, both vocal and nonvocal. But contrary to long-held beliefs among students of human prehistory, neither of those communicative capabilities first arose with humans; they, too, are descended from hemispheric specializations that first appeared in animals that lived long before our species emerged.

In birds, for instance, studies have shown that the left hemisphere controls singing. In sea lions, dogs and monkeys, the left hemisphere controls the perception of calls by other members of the same species. One of us (Rogers), in collaboration with Michelle A. Hook-Costigan, now at Texas A&M University, observed that common marmosets open the right side of their mouths  wider than the left side when making friendly calls to other marmosets. People also generally open the right side of their mouths to a greater extent than the left when they speak—the result of greater activation of the right side of the face by the left hemisphere.

Little is universal in nature, though, and in some animals a vocal response to highly emotional circumstances has also been linked to the left brain, not—as one might expect—to the right. When a male frog is clasped from behind and held by a rival male, for instance, the left hemisphere seems to control the vocal responses of the first frog. The left hemisphere in mice controls the reception of distress calls from infant mice, and in gerbils it controls the production of calls during copulation. But those animals may be exceptions. In humans and monkeys—and perhaps in most other animals—the right brain takes control in highly emotional vocalizing; the left brain sticks to the routine.

Nonvocal communication in humans has evolutionary antecedents as well. Not only do chimpanzees tend to be right-handed when they manipulate objects, but they also favor the right hand for communicative gestures. Gorillas, too, tend to incorporate the right hand into complex communications that also involve the head and the mouth. Adrien Meguerditchian and Jacques Vauclair, both at the University of Provence in France, have even observed a right-handed bias for one manual communication (patting the ground) in baboons.

The evolutionary significance of all this becomes clear as soon as one notes that humans also tend to make communicative gestures with the right hand. The lateralized behavior we share with baboons suggests that right-handed communications arose with the first appearance of the monkeylike ancestor we share with baboons. That creature emerged perhaps 40 million years ago—well before hominids began to evolve.

Evolution of Speech A fundamental question remains: Just how could any of the behaviors already controlled by the left brain—feeding, vocalizing, communicating with the right hand—have been modified to become speech—one of the most momentous steps in the history of life on earth?

One of us (MacNeilage) has hypothesized that it required the evolution of the syllable, the basic organizational unit underlying a stream of speech in time. The typical syllable is a rhythmic alternation between consonants and vowels. (Consonants are the sounds created when the vocal tract is momentarily closed or almost closed; vowels are the sounds created by resonance with the shape of the vocal tract as air flows relatively freely out through the open mouth.) The syllable may have evolved as a by-product of the alternate raising (consonant) and lowering (vowel) of the mandible, a behavior already well established for chewing, sucking and licking. A series of these mouth cycles, produced as lip smacks, may have begun to serve among early humans as communication signals, just as they do to this day among many other primates.

Somewhat later the vocalizing capabilities of the larynx could have paired with the communicative lip smacks to form spoken syllables. Syllables were perhaps first used to symbolize individual concepts, thus forming words. Subsequently, the ability to form sentences (language) presumably evolved when early humans combined the two kinds of words that carry the main meaning of sentences: those for objects (nouns) and those for actions (verbs).

The Right Hemisphere What about the second half of our hypothesis? How strong is the evidence that, early in vertebrate evolution, the right hemisphere specialized in detecting and responding to unexpected stimuli? In what ways has that underlying specialization evolved and been transformed?

One set of findings that lend strong support to our hypothesis comes from studies of the reactions to predators by various animals. After all, few events in ancient vertebrate environments could have been more unexpected and emotion-laden than the surprise appearance of a deadly predator. Sure enough, fishes, amphibians, birds and mammals all react with greater avoidance to predators seen in the left side of their visual field (right side of the brain) than in their right visual field.

Evidence that the same hemispheric specialization for reactions holds for humans comes from brain-imaging studies. In a summary of those studies, Michael D. Fox and his colleagues at Washington University in St. Louis conclude that humans possess an “attentional system” in the right hemisphere that is particularly sensitive to unexpected and “behaviorally relevant stim­uli”—or in other words, the kind of stimuli that say, in effect, Danger ahead! The existence of such an attentional system helps to make sense of an otherwise inexplicable human propensity: in the laboratory, even right-handed people respond more quickly to unexpected stimuli with their left hand (right hemisphere) than with their right hand.

Even in nonthreatening circumstances, many vertebrates keep a watchful left eye on any visible predators. This early right-hemisphere specialization for wariness in the presence of predators also extends in many animals to aggressive behavior. Toads, chameleons, chicks and baboons are more likely to attack members of their own species to their left than to their right.

In humans the relatively primitive avoidance and wariness behaviors that manifest right-hemisphere attentiveness in nonhuman animals have morphed into a variety of negative emotions. Nineteenth-century physicians noticed that patients complained more often of hysterical limb paralyses on the left side than on the right. There is some evidence for right-hemisphere control of emotional cries and shouts in humans—in striking contrast with the emotionally neutral vocalizations controlled by the left hemisphere. People are more likely to become depressed after damage to the left hemisphere than to the right. And in states of chronic depression the right hemisphere is more active than the left.

Recognizing Others Along with the sudden appearance of a predator, the most salient environmental changes to which early vertebrates had to react quickly were en­counters with others of their own species. In fishes and birds the right hemisphere recognizes social companions and monitors social behavior that might require an immediate reaction. Hence, the role of the right hemisphere in face perception must have descended from abilities of relatively early vertebrates to recognize the visual appearance of other individuals of their species.

For example, only some species of fishes—among the earliest evolving vertebrates—may be able to recognize individual fish, but birds in general do show a right-hemisphere capacity to recognize individual birds. Keith M. Kendrick of the Babraham Institute in Cambridge, England, has shown that sheep can recognize the faces of other sheep (and of people) from memory and that the right hemisphere is preferentially involved. Charles R. Hamilton and Betty A. Vermeire, both at Texas A&M, have observed similar behavior in monkeys.

In humans neuroscientists have recently recognized that the right hemisphere specializes in face recognition. Prosopagnosia, a neurological disorder that impairs that ability, is more often a result of damage to the right hemisphere than to the left. Extending face recognition to what seems another level, both monkeys and humans interpret emotional facial expressions more accurately with the right hemisphere than with the left. We think that this ability is part of an ancient evolutionary capacity of the right hemisphere for determining identity or familiarity—for judging whether a present stimulus, for instance, has been seen or encountered before.

Global and Local We have argued for a basic distinction between the role of the left hemisphere in normal action and the role of the right hemisphere in unusual circumstances. But investigators have highlighted additional dichotomies of hemispheric function as well. In humans the right hemisphere “takes in the whole scene,” attending to the global aspects of its environment rather than focusing on a limited number of features. That capacity gives it substantial advantages in analyzing spatial relations. Memories stored by the right hemisphere tend to be organized and recalled as overall patterns rather than as a series of single items. In contrast, the left hemisphere tends to focus on local aspects of its environment.

Striking evidence for the global-local dichotomy in humans has been brought to light by a task invented by David Navon of the University of Haifa in Israel. Brain-damaged patients are asked to copy a picture in which 20 or so small copies of the uppercase letter A have all been arranged to form the shape of a large capital H. Patients with damage to the left hemisphere often make a simple line drawing of the H with no small A letters included; patients with damage to the right hemisphere scatter small A letters unsystematically all over the page.

A similar dichotomy has been detected in chickens, suggesting its relatively early evolution. Richard J. Andrew of the University of Sussex in England and one of us (Vallortigara) have discovered that, as in humans, the domestic chick pays special attention to broad spatial relations with its right hemisphere. Moreover, chicks with the right eye covered, hence receiving input only to the right hemisphere, show interest in a wide range of stimuli, suggesting they are attending to their global environment. Chicks that can attend only with the left hemisphere (left eye covered) focus only on specific, local landmark features.

Why Do Hemispheres Specialize? Why have vertebrates favored the segregation of certain functions in one or the other half of the brain? To assess an incoming stimulus, an organism must carry out two kinds of analyses simultaneously. It must estimate the overall novelty of the stimulus and take decisive emergency action if needed (right hemisphere). And it must determine whether the stimulus fits some familiar category, so as to make whatever well-established response, if any, is called for (left hemisphere).

To detect novelty, the organism must attend to features that mark an experience as unique. Spatial perception calls for virtually that same kind of “nose for novelty,” because almost any standpoint an animal adopts results in a new configuration of stimuli. That is the function of the right hemisphere. In contrast, to categorize an experience, the organism must recognize which of its features are recurring, while ignoring or discarding its unique or idiosyncratic ones. The result is selective attention, one of the brain’s most important capabilities. That is the function of the left hemisphere.

Perhaps, then, those hemispheric specializations initially evolved because collectively they do a more efficient job of processing both kinds of information at the same time than a brain without such specialized systems. To test this idea, we had to compare the abilities of animals having lateralized brains with animals of the same species having nonlateralized brains. If our idea was correct, those with lateralized brains would be able to perform parallel functions of the left and right hemisphere more efficiently than those with nonlateralized brains.

Fortunately, one of us (Rogers) had already shown that by exposing the embryo of a domestic chick to light or to dark before hatching, she could manipulate the development of hemispheric specialization for certain functions. Just before hatching, the chick embryo’s head is naturally turned so that the left eye is covered by the body and only the right eye can be stimulated by light passing through the egg shell. The light triggers some of the hemispheric specializations for visual processing to develop. By incubating eggs in the dark, Rogers could prevent the specializations from developing. In particular, she found, the dark treatment prevents the left hemisphere from developing its normal superior ability to sort food grains from small pebbles, and it also prevents the right hemisphere from being more responsive than the left to predators.

Rogers and Vallortigara, in collaboration with Paolo Zucca of the University of Teramo in Italy, tested both kinds of chicks on a dual task: the chicks had to find food grains scattered among pebbles while they monitored for the appearance of a model predator overhead. The chicks incubated in light could perform both tasks simultaneously; those incubated in the dark could not—thereby confirming that a lateralized brain is a more efficient processor.

Social “Symmetry Breaking” Enabling separate and parallel processing to take place in the two hemispheres may increase brain efficiency, but it does not explain why, within a species, one or the other specialization tends to predominate. Why, in most animals, is the left eye (and the right hemisphere) better suited than the right eye (and the left hemisphere) for vigilance against predation? What makes the predominance of one kind of handedness more likely than a symmetric, 50–50 mixture of both?

From an evolutionary standpoint a “broken” symmetry, in which populations are made up mainly of left types or mainly of right types, could be disadvantageous because the behavior of individuals would be more predictable to predators. Predators could learn to approach on the prey’s less vigilant side, thereby reducing the chance of being detected. The uneven proportion of left- and right-type individuals in many populations thus indicates that the imbalance must be so valuable that it persists despite the increased vulnerability to predators. Rogers and Vallortigara have suggested that, among social animals, the advantage of conformity may lie in knowing what to expect from others of one’s own species.

Together with Stefano Ghirlanda of the Universities of Stockholm in Sweden and of Bologna in Italy, Vallortigara recently showed mathe­matically that populations dominated by left-type or by right-type individuals can indeed arise spontaneously if such a population has frequency-dependent costs and benefits. The mathematical theory of games often shows that the best course of action for an individual may depend on what most other members of its own group decide to do. Applying game theory, Ghirlanda and Vallortigara demonstrated that left- or right-type behavior can evolve in a population under social selection pressures—that is, when asymmetrical individuals must coordinate with others of their species. For example, one would expect schooling fish to have evolved mostly uniform turning preferences, the better to remain together as a school. Solitary fish, in contrast, would probably vary randomly in their turning preferences, because they have little need to swim together. This is in fact the case.

With the realization that the asymmetrical brain is not specific to humans, new questions about a number of higher human functions arise: What are the relative roles of the left and right hemispheres in having self-awareness, consciousness, empathy or the capacity to have flashes of insight? Little is known about those issues. But the findings we have detailed suggest that these functions—like the other human phenomena discussed here—will be best understood in terms of the descent with modification of prehuman capabilities.

Did the Syllable Evolve from Chewing? According to one of the authors (MacNeilage), the origin of human speech may be traceable to the evolution of the syllable—typically an alternation between consonant and vowel. In the word “mama,” for instance, each syllable begins with the consonant sound [m] and ends with the vowel sound [a]. As the cutaway diagrams show, the [m] sound is made by temporarily raising the jaw, or lower mandible, and stopping the flow of air from the lungs by closing the lips (below left). To make the following vowel sound [a], the jaw drops and air flows freely through the vocal tract (below right). MacNeilage has thus proposed that the making of syllabic utterances is an evolutionary modification of routine chewing behavior, which first evolved in mammals 200 million years ago.

A Lateralized Brain Is More Efficient One of the authors (Rogers) discovered that if she exposed chick embryos to light or to dark before they hatched, she could control whether the two halves of the chick brains developed their specializations for visual processing—that is, whether the chicks hatched with weakly or strongly lateralized brains. Rogers and another one of the authors (Vallortigara), with Paolo Zucca of the University of Teramo in Italy, then compared normal, strongly lateralized chicks with weakly lateralized chicks on two tasks. One task was to sort food grains from small pebbles (usually a job for the left hemisphere); the other task was to respond to a model of a predator (a cutout in the shape of a hawk) that was passed over the chicks (usually a task for the right hemisphere). The weakly lateralized chicks had no trouble learning to tell grains from pebbles when no model hawk was present. But when the hawk “flew” overhead, they frequently failed to detect it, and they were much slower than normal chicks in learning to peck at grains instead of pebbles. In short, without the lateral specializations of their brain, the chicks could not attend to two tasks simultaneously.

Note: This article was originally printed with the title, "Origins of the Left and Right Brain."

Left Brain, Right Brain: An Outdated Argument

• By Kevin Boehm
• April 15, 2012

“I am definitely a left-brained person — I am not very artistic.” How many times have we characterized ourselves as either left-brained and logical people or right-brained and creative people? This popular myth, which conjures up an image of one side of our brains crackling with activity while the other lies dormant, has its roots in outdated findings from the 1970s, and it seems to imply that humans strongly favor using one hemisphere over the other. More recent findings have shown that although there are indeed differences between the hemispheres, they may not be as clear-cut as we once thought.

Our personalities and abilities are not determined by favoring one hemisphere over the other — that much is certain. Many other functions, however, such as response to danger and language generation, are lateralized in the brain. Researchers hypothesize that these differences arose from early vertebrates. Originally, it seems that the right hemisphere began to respond more quickly to danger. In fact, when we are suddenly confronted by a dangerous stimulus, we will respond more quickly with our left hand, which is controlled by the right hemisphere. The left hemisphere, on the other hand, has developed to handle more common, routine tasks, such as feeding and hand control. Since this hemisphere controls the right hand, a strong right-handed preference has arisen in most of us, providing one explanation of why most people are right-hand dominant.

Language is another process that is lateralized in the brain, though a study conducted by researchers at Ghent University has shown that the asymmetry differs when generating versus receiving language. When children were shown images and asked to tell a story about them, function was lateralized strongly in the left hemisphere for over 90 percent of participating children. However, when asked to listen to an emotional story, both hemispheres of the brain were activated to a similar degree as planning and articulation require more processing involving more regions on both sides of the brain. The stories the children listened to, unlike the pictures, were emotional, which may indicate that the observed involvement of the right hemisphere is linked to emotional regulation.

Olivia Farr, a neuroscience Ph.D. candidate at the Yale School of Medicine, explains that this language lateralization is the source of many generalizations. “In some of the first studies conducted on hemispheric lateralization, split-brained patients without an intact corpus callosum, or bridge between the two hemispheres, were examined,” says Farr. Because visual information from the right eye goes to the left hemisphere, when split-brained patients saw a word with their right eye, they could speak it but not draw it. When the patients saw a word with the left eye, they could draw but not speak it. These results contributed to the belief that hemispheres operate independently of each other for most tasks, which then developed into the myth of being exclusively left-brained or right-brained. There was so little known about the brain that it was convenient to attribute poorly understood traits, such as personality or thinking habits, to a clear-cut difference in lateralization. However, “we now know that hemispheres are always communicating, and that even these lateralization rules don’t always apply,” Farr affirms.

Hemispheres sometimes do perform tasks nearly independently, but the integration of the two yields some of our most uniquely human characteristics. For example, when we make errors, our realization and ability to correct them is a result of the synergy of the two halves of our brain. In fact, patients with damage to the corpus callosum have difficulties correcting their errors as compared to patients with intact corpora callosa, further suggesting that the two halves of the brain are both involved in processing the error.

Even though some tasks usually occur preferentially in one half of the brain, it is possible for the part directly opposite to take control of the process. Such a process takes time, but after damage in the left inferior frontal gyrus (referred to as Broca’s area) — a region of the brain linked to speech production — researchers have found that activity in the right inferior frontal gyrus begins to increase during language generation. Our brains have enough plasticity to adapt to damage and change conformations, even as adults.

Knowing that language processing usually occurs on the left side of the brain and response to danger generally occurs on the right does not comprehensively summarize our beings. Lateralization of the brain is still not well understood, and there are very few, if any, hard and fast rules of lateralization that actually make an impact on our behavior. We are still every bit as human and unpredictable as before, but we now understand a bit more of what makes us that way.

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Left Brain, Right Brain: Facts and Fantasies

* E-mail: [email protected]

Affiliation School of Psychology, University of Auckland, Auckland, New Zealand

• Michael C. Corballis

Published: January 21, 2014

• https://doi.org/10.1371/journal.pbio.1001767
• Reader Comments

Handedness and brain asymmetry are widely regarded as unique to humans, and associated with complementary functions such as a left-brain specialization for language and logic and a right-brain specialization for creativity and intuition. In fact, asymmetries are widespread among animals, and support the gradual evolution of asymmetrical functions such as language and tool use. Handedness and brain asymmetry are inborn and under partial genetic control, although the gene or genes responsible are not well established. Cognitive and emotional difficulties are sometimes associated with departures from the “norm” of right-handedness and left-brain language dominance, more often with the absence of these asymmetries than their reversal.

Citation: Corballis MC (2014) Left Brain, Right Brain: Facts and Fantasies. PLoS Biol 12(1): e1001767. https://doi.org/10.1371/journal.pbio.1001767

Copyright: © 2014 Michael C Corballis. This is an open-access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: Some of the research summarised in this article was funded by Contract UOA from the Marsden Fund of the Royal Society of New Zealand. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The author has declared that no competing interests exist.

“That raven on yon left-hand oak (Curse his ill-betiding croak) Bodes me no good!” —from Fables, by John Gay (1688–1732)

Introduction

The most obvious sign that our brains function asymmetrically is the near-universal preference for the right hand, which goes back at least as far as the historical record takes us, and has long been a powerful source of symbolism, with the dexterous right associated with positive values and the sinister left with negative ones [1] . This has often led to stigmatization of left-handed individuals, sometimes forcing them to switch hand use, occasionally with grievous consequences. Superstitions about left and right were compounded by the discovery, in the 1860s, that speech was based predominantly in the left hemisphere of the brain [2] . Since language itself is uniquely human, this reinforced the idea that brain asymmetry more generally is a distinctive mark of being human [3] . Because the left hemisphere also controls the dominant right hand, it came to be widely regarded as the dominant or major hemisphere, and the right as nondominant or minor. Nevertheless, further evidence that the right hemisphere was the more specialized for perception and emotion also led to speculation, some of it far-fetched, about the complementary roles of the two sides of the brain in maintaining psychological equilibrium [4] .

Interest flagged for a while, but was revived a century later, in the 1960s, with the study of patients who had undergone split-brain surgery, in which the main commissures connecting the two hemispheres were cut as a means of controlling intractable epilepsy. Testing of each disconnected hemisphere again revealed the left to be specialized for language and the right for emotional and nonverbal functions [5] , [6] . This work won Roger W. Sperry the Nobel Prize for Physiology and Medicine in 1981, but again led to speculation, most of it exaggerated or ill-founded, about the complementary functions of the two sides of the brain.

One popular example is Betty Edwards' Drawing on the Right Side of the Brain , first published in 1979 but now in its fourth edition [7] , which epitomizes the popular view that the right hemisphere is responsible for creativity. Brain imaging shows, though, that creative thought activates a widespread network, favoring neither hemisphere [8] . A more recent example is Iain McGilchrist's 2009 book The Master and His Emissary , which draws on cerebral asymmetry in a sweeping account of the forces that shaped Western culture, and provocatively declares the right hemisphere to be the dominant one (“the master”) [9] . Although widely acclaimed, this book goes far beyond the neurological facts. Polarities of left and right brain are broadly invoked in art, business, education, literary theory, and culture, but owe more to the power of myth than to the scientific evidence [10] .

Evolution of Brain Asymmetries, with Implications for Language

One myth that persists even in some scientific circles is that asymmetry is uniquely human [3] . Left–right asymmetries of brain and behavior are now known to be widespread among both vertebrates and invertebrates [11] , and can arise through a number of genetic, epigenetic, or neural mechanisms [12] . Many of these asymmetries parallel those in humans, or can be seen as evolutionary precursors. A strong left-hemispheric bias for action dynamics in marine mammals and in some primates and the left-hemisphere action biases in humans, perhaps including gesture, speech, and tool use, may derive from a common precursor [13] . A right-hemisphere dominance for emotion seems to be present in all primates so far investigated, suggesting an evolutionary continuity going back at least 30 to 40 million years [14] . A left-hemisphere dominance for vocalization has been shown in mice [15] and frogs [16] , and may well relate to the leftward dominance for speech—although language itself is unique to humans and is not necessarily vocal, as sign languages remind us. Around two-thirds of chimpanzees are right-handed, especially in gesturing [17] and throwing [18] , and also show left-sided enlargement in two cortical areas homologous to the main language areas in humans—namely, Broca's area [19] and Wernicke's area [20] (see Figure 1 ). These observations have been taken as evidence that language did not appear de novo in humans, as argued by Chomsky [21] and others, but evolved gradually through our primate lineage [22] . They have also been interpreted as evidence that language evolved not from primate calls, but from manual gestures [23] – [25] .

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Image credit: Todd Preuss, Yerkes Primate Research Center ( http://commons.wikimedia.org/wiki/File:Human_and_chimp_brain.png ).

https://doi.org/10.1371/journal.pbio.1001767.g001

Some accounts of language evolution (e.g., [25] ) have focused on mirror neurons, first identified in the monkey brain in area F5 [26] , a region homologous to Broca's area in humans, but now considered part of an extensive network more widely homologous to the language network [27] . Mirror neurons are so called because they respond when the monkey performs an action, and also when they see another individual performing the same action. This “mirroring” of what the monkey sees onto what it does seems to provide a natural platform for the evolution of language, which likewise can be seen to involve a mapping of perception onto production. The motor theory of speech perception, for example, holds that we perceive speech sounds according to how we produce them, rather than through acoustic analysis [28] . Mirror neurons in monkeys also respond to the sounds of such physical actions as ripping paper or dropping a stick onto the floor, but they remain silent to animal calls [29] . This suggests an evolutionary trajectory in which mirror neurons emerged as a system for producing and understanding manual actions, but in the course of evolution became increasingly lateralized to the left brain, incorporating vocalization and gaining grammar-like complexity [30] . The left hemisphere is dominant for sign language as for spoken language [31] .

Mirror neurons themselves have been victims of hyperbole and myth [32] , with the neuroscientist Vilayanur Ramachandran once predicting that “mirror neurons will do for psychology what DNA did for biology” [33] . As the very name suggests, mirror neurons are often taken to be the basis of imitation, yet nonhuman primates are poor imitators. Further, the motor theory of speech perception does not account for the fact that speech can be understood by those deprived of the ability to speak, such as those with damage to Broca's area. Even chimpanzees [34] and dogs [35] can learn to respond to simple spoken instructions, but cannot produce anything resembling human speech. An alternative is that mirror neurons are part of a system for calibrating movements to conform to perception, as a process of learning rather than direct imitation. A monkey repeatedly observes its hand movements to learn to reach accurately, and the babbling infant calibrates the production of sounds to match what she hears. Babies raised in households where sign language is used “babble” by making repetitive movements of the hands [36] . Moreover, it is this productive aspect of language, rather than the mechanisms of understanding, that shows the more pronounced bias to the left hemisphere [37] .

Inborn Asymmetries

Handedness and cerebral asymmetries are detectable in the fetus. Ultrasound recording has shown that by the tenth week of gestation, the majority of fetuses move the right arm more than the left [38] , and from the 15th week most suck the right thumb rather than the left [39] —an asymmetry strongly predictive of later handedness [40] (see Figure 2 ). In the first trimester, a majority of fetuses show a leftward enlargement of the choroid plexus [41] , a structure within the ventricles known to synthesize peptides, growth factors, and cytokines that play a role in neurocortical development [42] . This asymmetry may be related to the leftward enlargement of the temporal planum (part of Wernicke's area), evident at 31 weeks [43] .

Image credit: jenny cu ( http://commons.wikimedia.org/wiki/File:Sucking_his_thumb_and_waving.jpg ).

https://doi.org/10.1371/journal.pbio.1001767.g002

In these prenatal brain asymmetries, around two-thirds of cases show the leftward bias. The same ratio applies to the asymmetry of the temporal planum in both infants and adults [44] . The incidence of right-handedness in the chimpanzee is also around 65–70 percent, as is a clockwise torque, in which the right hemisphere protrudes forwards and the left hemisphere rearwards, in both humans and great apes [45] . These and other asymmetries have led to the suggestion that a “default” asymmetry of around 65–70 percent, in great apes as well as humans, is inborn, with the asymmetry of human handedness and cerebral asymmetry for language increased to around 90 percent by “cultural literacy” [46] .

Variations in Asymmetry

Whatever their “true” incidence, variations in handedness and cerebral asymmetry raise doubts as to the significance of the “standard” condition of right-handedness and left-cerebral specialization for language, along with other qualities associated with the left and right brains that so often feature in popular discourse. Handedness and cerebral asymmetry are not only variable, they are also imperfectly related. Some 95–99 percent of right-handed individuals are left-brained for language, but so are about 70 percent of left-handed individuals. Brain asymmetry for language may actually correlate more highly with brain asymmetry for skilled manual action, such as using tools [47] , [48] , which again supports the idea that language itself grew out of manual skill—perhaps initially through pantomime.

Even when the brain is at rest, brain imaging shows that there are asymmetries of activity in a number of regions. A factor analysis of these asymmetries revealed four different dimensions, each mutually uncorrelated. Only one of these dimensions corresponded to the language regions of the brain; the other three had to do with vision, internal thought, and attention [49] —vision and attention were biased toward the right hemisphere, language and internal thought to the left. This multidimensional aspect throws further doubt on the idea that cerebral asymmetry has some unitary and universal import.

Handedness, at least, is partly influenced by parental handedness, suggesting a genetic component [50] , but genes can't tell the whole story. For instance some 23 percent of monozygotic twins, who share the same genes, are of opposite handedness [51] . These so-called “mirror twins” have themselves fallen prey to a Through the Looking Glass myth; according to Martin Gardner [52] , Lewis Carroll intended the twins Tweedledum and Tweedledee in that book to be enantiomers, or perfect three-dimensional mirror images in bodily form as well as in hand and brain function. Although some have argued that mirroring arises in the process of twinning itself [53] , [54] , large-scale studies suggest that handedness [55] , [56] and cerebral asymmetry [57] in mirror twins are not subject to special mirroring effects. In the majority of twins of opposite handedness the left hemisphere is dominant for language in both twins, consistent with the finding that the majority of single-born left-handed individuals are also left-hemisphere dominant for language. In twins, as in the singly born, it is estimated that only about a quarter of the variation in handedness is due to genetic influences [56] .

The manner in which handedness is inherited has been most successfully modeled by supposing that a gene or genes influence not whether the individual is right- or left-handed, but whether a bias to right-handedness will be expressed or not. In those lacking the “right shift” bias, the direction of handedness is a matter of chance; that is, left-handedness arises from the lack of a bias toward the right hand, and not from a “left-hand gene.” Such models can account reasonably well for the parental influence [58] – [60] , and even for the relation between handedness and cerebral asymmetry if it is supposed that the same gene or genes bias the brain toward a left-sided dominance for speech [60] , [61] . It now seems likely that a number of such genes are involved, but the basic insight that genes influence whether or not a given directional bias is expressed, rather than whether or not it can be reversed, remains plausible (see Box 1 ).

Box 1. The Genetics of Handedness and Cerebral Asymmetry

Linkage analyses have often revealed candidate laterality genes, but all too often these fail in follow-up analysis—a common problem in the search for genes related to human behavior. Part of the problem is the sheer immensity of the genome, which means that candidates are likely to surface by chance, and the problem is compounded by the likelihood of a strong chance element in the determination of handedness itself. With appropriate statistical control, several large-scale genome-wide studies have failed to reveal any single locus to be significantly associated with handedness [68] , [69] , including one study [70] based on a large sample of twins, which also failed specifically to support the single-gene model developed by McManus [60] , or weaker versions of that model. The authors of one study estimate that as many as 40 different loci may be involved [71] , but note that it would be difficult to distinguish multilocus models from a single-gene model, such as that of McManus, in terms of handedness pedigrees.

The study of one candidate gene, PCSK6 , has led to some insight as to polygenic control of handedness. Across three independent samples of individuals with dyslexia, a genome-wide assay revealed the minor allele at the rs11855415 locus within this gene to be significantly associated with increased right-handedness [72] . This allele was not significantly associated with handedness in a large sample from the general population. Another targeted search within the PCSK6 gene failed to confirm a role for rs11855415 in a large sample from the general population, but revealed that a tandem repeat polymorphism at another locus, rs10523972, was associated with the degree, but not the direction, of handedness [73] . PCSK6 is involved in regulating NODAL, which plays a role in the development of the left–right axis in vertebrates, and knock-out of PCSK6 in mice results in defects in the placement of normally asymmetrical internal organs. Several other genes in the pathway that leads to anomalies of left–right development in mice proved to be associated as a group with human handedness in the general population, leading to the suggestion that handedness is indeed a polygenic trait partly controlled by the genes that establish body asymmetry early in development [74] .

Another gene of interest is LRRTM1 , which has been associated with handedness and schizophrenia when inherited through the father [75] , where a particular haplotype consisting of minor alleles at three locations within the gene significantly shifted handedness to the left—a finding partially confirmed elsewhere [76] . Again, though, LRRTM1 does not stand out in genome-wide assays in samples from the general population. Nevertheless, schizophrenia has long been associated with increased left-handedness or ambidexterity [77] , [78] , as have schizotypy and tendencies to magical thinking [79] – [81] . Just as the association of PCSK6 with dyslexia led to suggestion of a polygenic pathway, so the association of LRRTM1 with schizophrenia may lead to other pathways influencing handedness and brain asymmetry.

Another suggestion is that cerebral asymmetry, and even a disposition to schizophrenia, was critical to human speciation, involving a rearrangement within the X and Y chromosomes, and that it was this event that constituted the supposed “big bang” that created language de novo in our species [82] . The idea that language emerged in this saltatory fashion, still championed by Chomsky [21] , is now widely questioned [83] , [84] . Linkage analysis gives little support to the involvement of the X and Y chromosomes, although one study has shown that repeats of a CAG sequence in the androgen receptor locus on the X chromosome are linked to handedness. In females the incidence of left-handedness increased with the number of repeats, while in males it was reduced with the number of repeats. This finding supports a role for testosterone in the determination of handedness [85] . In recent formulations of the X–Y theory, it has been proposed that handedness and cerebral asymmetry are facultative traits, universally encoded in the human genome, and that the variations giving rise to schizophrenia or anomalies of handedness and cerebral asymmetry are epigenetic, and therefore not coded in the nucleotide sequence [86] . It appears that epigenetic change through DNA methylation can be transmitted between generations [87] , which might explain pedigree effects that are not detected in linkage analyses.

Another gene that has been linked to language evolution is the FOXP2 gene, following the discovery that about half the members of an extended family possessed a mutation of this gene that caused a severe deficit in articulating speech [88] . Unlike the unaffected family members, they all failed to show activation of Broca's area when asked to silently generate words, and indeed showed no consistent asymmetry at all [89] . A more recent study also shows widespread anatomical differences between the affected and unaffected family members, including bilateral reduction of the caudate nucleus in the affected members, along with a reduction of grey matter in Broca's area on the left [90] . All of the affected individuals are right-handed, though, so the effect of the mutation appears to involve the brain circuits involved in speech, and possibly more generally in language and other motor skills, but not in handedness itself. Although highly conserved in mammalian evolution, the human FOXP2 gene differs in two locations from that in the chimpanzee, leading to the suggestion that it may have played a role in the evolution of language [91] . Evidence that the most recent mutation was also present in Neanderthal DNA [92] again argues against the “big bang” theory that language evolved uniquely in humans.

Genetic considerations aside, departures from right-handedness or left-cerebral dominance have sometimes been linked to disabilities. In the 1920s and 1930s, the American physician Samuel Torrey Orton attributed both reading disability and stuttering to a failure to establish cerebral dominance [62] . Orton's views declined in influence, perhaps in part because he held eccentric ideas about interhemispheric reversals giving rise to left–right confusions [63] , and in part because learning-theory explanations came to be preferred to neurological ones. In a recent article, Dorothy Bishop reverses Orton's argument, suggesting that weak cerebral lateralization may itself result from impaired language learning [64] . Either way, the idea of an association between disability and failure of cerebral dominance may be due for revival, as recent studies have suggested that ambidexterity, or a lack of clear handedness or cerebral asymmetry, is indeed associated with stuttering [65] and deficits in academic skills [66] , as well as mental health difficulties [67] and schizophrenia (see Box 1 ).

Although it may be the absence of asymmetry rather than its reversal that can be linked to problems of social or educational adjustment, left-handed individuals have often been regarded as deficient or contrarian, but this may be based more on prejudice than on the facts. Left-handers have excelled in all walks of life. They include five of the past seven US presidents, sports stars such as Rafael Nadal in tennis and Babe Ruth in baseball, and Renaissance man Leonardo da Vinci, perhaps the greatest genius of all time.

Author Contributions

The author(s) have made the following declarations about their contributions: Conceived and written by: MC.

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Left Brain - Right Brain

Reviewed by Psychology Today Staff

The human brain includes two hemispheres connected by a bundle of nerves. The left hemisphere controls movement for the right side of the body, while the right hemisphere directs the left side. The hemispheres specialize in distinct mental functions—different aspects of visual perception, for example—but most behaviors and abilities require activity in both halves of the brain.

• How Both Sides Work Together
• “Left-Brained” and “Right-Brained” People

Both sides of the brain collaborate to handle major functions such as language processing and vision. But they are also, to a degree, specialized. Some areas of the brain are more active than others during particular tasks, and one hemisphere may be more involved than the other in specific parts of a larger mental operation.

For example, Broca’s area and Wernicke’s area are both linked to language and are most commonly located on the left side of the brain. Yet the right hemisphere is also known to play a role in language processing. Meanwhile, the limbic system—which includes the amygdalae and hippocampi and is involved in functions such as emotion and memory —resides on both sides of the brain.

In language processing, it is usually the left brain that properly orders words during speech, while in visual perception, it registers the locations of objects in space relative to other objects. 

The right brain, like the left brain , supports language, including in processing the correct meaning of a set of words with more than one possible implication (as in the case of figurative speech). And in visual perception, it processes the distance between objects.

Each brain hemisphere controls the movement of the opposite side of the body. In left-handed people, the motor cortex in the right hemisphere is dominant for fine motor behaviors, such as writing with a pencil. The reverse is true for right-handed people—the left hemisphere is stronger when it comes to such movements.

A widespread myth suggests that some people, whose left hemisphere is dominant overall, are more quantitative, logical, and analytical, while right-brained individuals are more emotional, intuitive, and creative. Like many ways of categorizing people, the left brain/right brain dichotomy is appealing , promising to teach individuals about how they think and why. But the reality of hemispheric specialization is much more complex than this popular concept suggests.

No. While the brain’s left and right hemispheres do handle distinct functions , their duties aren’t strictly divided according to broad categories like “logical” or “creative.” People can't be split neatly into groups with special strengths based on one hemisphere being more dominant.

The “left-brained” type has been described as logical, analytical, and detail-oriented, while “right-brained” people have been characterized as creative and intuitive—though other supposed traits have been attributed to each. (In any case, the "left-brained" and "right-brained" types are not scientifically supported .)

The concept of “left-brained” and “right-brained” individuals appears to stem from research in the 1960s on “split-brain” patients, whose corpus callosum (the bridge between hemispheres) had been separated. The research revealed that patients responded in different ways to stimuli such as images, depending on which brain hemisphere perceived them.

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Lateralization of Brain Function & Hemispheric Specialization

Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

Learn about our Editorial Process

Saul Mcleod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul Mcleod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

On This Page:

Lateralization of brain function is the view that distinct brain regions perform certain functions.

For instance, it is believed that different brain areas are responsible for controlling language, formulating memories, and making movements.

If a certain area of the brain becomes damaged, the function associated with that area will also be affected.

It contrasts with the holistic theory of the brain that all parts of the brain are involved in the processing of thought and action.

Left brain vs. Right brain

The human brain is split into two hemispheres, right and left. They are joined together by the corpus callosum, a bundle of nerve fibers located in the middle of the brain.

Hemispheric lateralization is the idea that each hemisphere is responsible for different functions . Each of these functions is localized to either the right or left side.

The left hemisphere is associated with language functions, such as formulating grammar and vocabulary and containing different language centers (Broca’s and Wernicke’s area).

The right hemisphere is associated with more visuospatial functions such as visualization, depth perception, and spatial navigation. These left and right functions are the cases in most people, especially right-handed people.

The brain contains cortices such as the visual, motor, and somatosensory cortices . These cortices are all contralateral, meaning that each hemisphere controls the opposite side of the body.

For example, the motor cortex in the left hemisphere controls the muscle movements of the right arm and leg. Likewise, damage to the right occipital lobe (responsible for vision) can result in loss of sight in the left field of vision.

Language Lateralization

Hemispheric lateralization is the idea that both hemispheres are functionally different and that certain mental processes and behaviors are mainly controlled by one hemisphere rather than the other.

There is evidence of some specialization of function, mainly regarding differences in language ability. Beyond that, however, the differences found have been minor. We know that the left hemisphere controls the right half of the body, and the right hemisphere controls the left half of the body.

Broca’s Area

Paul Broca was a French physician and one of the earlier advocators for lateralization of brain function. In 1861, Broca met a patient who he would refer to as ‘Tan.’

At the time, there was a lot of debate as to whether there was the localization of function within the brain or if the whole brain was utilized in performing every function.

Broca described the patient ‘Tan,’ who was named this due to this being the only word they could say. Often this patient would repeat the word twice, saying ‘Tan Tan.’

When ‘Tan’ died, a post-mortem of his brain revealed damage to a part of his left frontal cortex. Broca found that other patients with similar problems to Tan had damage to the same region.

It was concluded that the damage to this region, then given the name ‘Broca’s area,’ was the reason for Tan’s language problems. Broca’s area is believed to be located in a part of the inferior frontal gyrus in the frontal lobe , on the left side of the majority of people.

This research largely supports the view that the role of language function is localized to the brain’s left hemisphere.

Broca’s area is associated with multiple language functions, including language comprehension and being able to articulate words.

This region is also associated with listening, as understanding words requires articulating them in your head. It has also been suggested to be active during planning, initiating, and understanding another’s movement.

Broca’s area may also contain mirror neurons as this area appears to be involved in observing people and imitating them (Amunts & Hari, 2005).

The term Broca’s Aphasia was used to describe the condition of Tan and Broca’s other patients. People who have damage to Broca’s area tend to have suffered a brain injury (e.g., through a stroke) which then affects this language area.

The main symptom of Broca’s aphasia is a deficit in spoken and written language production. A person with damage to this area would likely be unable to articulate words or be able to string a coherent sentence together.

Speaking in an abnormal tone or rhythm can also be a symptom of this damage, as well as speech being repetitive, disordered grammar, and a disordered structure of individual words.

Finally, damage can also result in transcortical motor aphasia, meaning the speech is non-fluent and often limited to two words at a time.

Wernicke’s Area

A few years after Broca’s discoveries, in 1876, German neurologist Carl Wernicke identified another region of the brain associated with language.

Wernicke identified that some of his patients were able to speak but were not able to actually comprehend language. When examining the brains of these patients, it was revealed that there were lesions at a junction of the upper temporal lobe in the left hemisphere.

This region was named Wernicke’s area and was described as an area where heard and seen words are understood and words selected for articulation.

This area also works together with Broca’s area. Wernicke’s area comprehends the language and chooses words, which are then sent to Broca’s area to be articulated.

Wernicke’s area contains motor neurons involved in speech comprehension and is surrounded by an area called Geschwind’s territory.

When a person hears words, Wernicke’s area associates the sounds with their meaning, to which neurons in Geschwind’s territory are thought to help by combining the many different properties of words (such as the sound and meaning) to provide fuller comprehension.

When a person speaks, however, this process happens in reverse as Wernicke’s area will find the right words to correspond to the thoughts to be expressed.

Wernicke’s Aphasia was coined to describe damage to Wernicke’s area. This is often thought to be damaged via head trauma or disease.

People who experience Wernicke’s aphasia may experience symptoms such as an inability to understand spoken language and speaking using inappropriate words.

Their sentences may not make sense. They may repeat words, make up meaningless words, or have sentences lacking meaning.

Most of the time, people with Wernicke’s aphasia often speak fluently, compared to Broca’s aphasia, where language is non-fluent or broken up.

Some patients may not even be aware that they have an issue with their speech and will believe they are speaking normally.

Research Studies

Split-brains.

Split-brain research demonstrates that the brain’s two hemispheres can operate independently when the corpus callosum, which connects them, is severed. This reveals lateralization of brain functions, with certain tasks predominantly managed by one hemisphere or another.

For instance, the left hemisphere typically handles language and logical processing, while the right is more involved in spatial and holistic processing.

As an outdated treatment for severe epilepsy, the corpus callosum was sliced, meaning the connections between the two hemispheres were halted.

People who undergo this procedure are known as split-brain patients. In the 1960s, neurobiologist Roger Sperry conducted experiments on these split-brain patients to test whether there was a localization of function in the hemispheres.

Sperry conducted many split-brain experiments, one being the ‘divided field experiment.’ An example of this experiment would be to project words on the right and left fields of vision while one eye is covered to test whether the patients can say the word.

They found that the patients could say the word presented on the right visual field, controlled by the left hemisphere and containing the language centers. The words presented on the left side, controlled by the right hemisphere, could not be spoken.

However, the patients would instead be able to draw the word that was shown on the left side or pick up the object of the word shown due to the right hemisphere being able to control motor movements of the left hand.

When asked why the patients chose or drew the objects, they were unable to say, suggesting that the right hemisphere (in most people) is unconscious, although the information it holds can affect behavior.

Another study by Gazzaniga (1983) conducted a similar experiment but used faces projected to both visual fields. It was found that faces on the left visual field, thus projecting to the right hemisphere, were recognized, but not through the right visual field to the left hemisphere.

This demonstrates that the right hemisphere may better recognize faces in general.

Although it is known that the lateralization of language functions is in the left hemisphere in most people, this lateralization may depend on personal handedness.

Szaflarski et al. (2002) used functional magnetic resonance imaging (fMRI) on individuals who were left-hand dominant while they completed language acquisition and non-linguistic tasks.

It was found through the fMRI that there was more activation in the right hemisphere of the participants, concluding that they had typical language dominance.

There is a question of whether or not lateralization of language function occurs from birth, or if this lateralization develops over time.

Olulade et al. (2020) aimed to study the lateralization of language development by using fMRI on children and adults completing language-based tasks.

The researchers found that in the youngest children (aged 4-6 years old), there was left and right hemispheric activation, so language was not lateralized to one hemisphere.

They also found that right-side activation significantly decreased with age, with over 60% of adults lacking any considerable right activation.

This study suggests that lateralization of language, predominately the left hemisphere, develops over time during childhood.

Emotion lateralization

A review of the literature investigating the lateralization of emotion in the brain found that the left and right hemispheres have different functions regarding emotions (Silberman & Weingartner, 1986).

It was suggested that the right hemisphere is better at controlling emotional expressions and recognizing emotions and is associated with feelings of negative emotions.

Meanwhile, the left hemisphere specialized in dealing with positive emotions. This implied that different functions of emotion lateralized to each hemisphere.

In support of this view, another study found that patients who had suffered trauma to their left frontal lobe, particularly their prefrontal cortex, experienced depression as a result (Paradiso et al., 1999).

Similarly, patients who had suffered damage to their right frontal lobes were found to be more likely to show signs of inappropriate cheerfulness and mania (Starkstein et al., 1989).

This supports the idea that the left hemisphere is lateralized to positive emotions while the right is lateralized to negative ones.

Gender Differences

There are several studies that support the notion that there are differences in the lateralization of function in the brains of males and females.

Tomasi and Volkow (2012) found that males had increased right lateralization of connectivity in areas of the temporal, frontal, and occipital cortices. In contrast, females had increased left lateralization of connectivity in the left frontal cortex.

It is suggested that differences in the lateralization of males’ and females’ brains may underlie some of the typical gender differences in cognitive styles.

For instance, females’ typical linguistic advantage over males may reflect increased left lateralization of language areas. In contrast, males’ typical advantage of visuospatial skills may reflect increased lateralization of right-side visuospatial areas (Clements et al., 2006).

Reber and Tranel (2017) reviewed studies of brain differences in males and females. They found a lot of evidence of a sex-related difference in an area of the brain called the ventral-medial prefrontal cortex (vmPFC), an area associated with decision-making and emotion.

Tranel et al. (2002) found that male patients with damage to their right vmPFC showed deficits in social, emotional, and decision-making skills than those with left-side damage.

However, the only female patient with right vmPFC damage displayed fewer deficits in all behavioral categories. This evidence implies that lateralization of higher cognitive functions depends on the sex of the individual.

Phineas Gage (1848)

The theory of brain localization is supported by the famous case study of Phineas Gage (1848) , an American railway construction foreman. During an accident, a large iron rod was driven completely through his head, destroying much of his brain’s left frontal lobe.

He survived the accident, but his personality changed; he became unstable and is reported not to have been able to hold down a job.

This supports the localization of functions theory as it shows that control of social behavior is located in the frontal cortex .

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Further Reading

• Gainotti, G. (2014). Why are the right and left hemisphere conceptual representations different?. Behavioral neurology, 2014.
• Macdonald, K., Germine, L., Anderson, A., Christodoulou, J., & McGrath, L. M. (2017). Dispelling the myth: Training in education or neuroscience decreases but does not eliminate beliefs in neuromyths. Frontiers in psychology , 8, 1314.
• Corballis, M. C. (2014). Left brain, right brain: facts and fantasies. PLoS Biol, 12 (1), e1001767.
• Nielsen, J. A., Zielinski, B. A., Ferguson, M. A., Lainhart, J. E., & Anderson, J. S. (2013). An evaluation of the left-brain vs. right-brain hypothesis with resting state functional connectivity magnetic resonance imaging. PloS one, 8 (8), e71275.

Encyclopedia of the Sciences of Learning pp 3226–3230 Cite as

Styles of Learning and Thinking: Hemisphericity Functions

• Kalpana Vengopal 2  
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Ways of learning and thinking

The differences in preference of the two hemispheres for retaining and processing of information in one’s own style of learning and thinking is known as styles of learning and thinking. Hemisphericity is the cerebral dominance of an individual in retaining and processing modes of information in his own style of learning and thinking.

Theoretical Background

Styles depend upon cerebral dominance of an individual in retaining and processing different modes of information in his own styles of learning and thinking. Styles indicate the hemisphericity functions of brain, and students learning strategy and information processing are based on the preferences of the brain area. Styles are propensities rather than abilities. They are the ways of directing the intellect which an individual finds comfortable. The style of learning and thinking are as important as levels of ability, and we ignore to identify and develop students’ thinking styles at...

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Fitzgerald, D., & Hattie, J. A. (1983). An evaluation of your style of learning and thinking inventory. British Journal of Educational Psychology, 53 , 336–346.

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Reynolds, C. R., & Torrance, E. P. (1978). Perceived changes in styles of learning and thinking (Hemisphericity) through direct and indirect training. Journal of Creative Behaviour, 12 , 245–252.

Venkataraman, D. (1994). Style of learning and thinking . New Delhi: M/s. Psy-Com Services.

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Vengopal, K. (2012). Styles of Learning and Thinking: Hemisphericity Functions. In: Seel, N.M. (eds) Encyclopedia of the Sciences of Learning. Springer, Boston, MA. https://doi.org/10.1007/978-1-4419-1428-6_1728

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Understanding the Right Brain: Characteristics, Functions, and Dominance

The human brain is a complex and fascinating organ that controls a vast array of physiological and cognitive functions . It is divided into two hemispheres , each with its unique set of functions and characteristics . The left hemisphere is primarily responsible for logical , analytical, and linear thinking , while the right hemisphere is associated with creativity , intuition , and holistic thinking. In recent years, there has been a growing interest in the right brain , with many people wondering what it entails to be a “right-brained” person. In this article, we will explore the characteristics, functions, dominance , and activities associated with the right brain.

What is the Right Brain?

The right brain is the hemisphere of the brain responsible for intuitive, creative, and subjective thinking. Unlike the left hemisphere, which uses language and logical thinking to interpret the world, the right hemisphere processes information holistically, considering all factors and context. The right brain is often associated with emotions , visual and spatial perception, and nonverbal communication.

What Are 3 Characteristics of the Right Brain?

The Right brain is rich in characteristics that distinguish it from the left brain. Here are three of the most notable ones:

Creativity – The right brain is often linked to creativity, and rightly so. This hemisphere of the brain can think outside the box and generate unique solutions to problems. Creative fields such as art, music, and dance are often dominated by right-brained individuals who have a natural talent for coming up with novel ideas.

Intuition – The right brain can process information holistically, taking into account all the factors that influence a situation. As such, it is often linked to intuition, which is the ability to understand something instinctively without the need for conscious reasoning.

Emotional Intelligence – The right brain is more receptive to emotional information than the left brain. It can process nonverbal communication, including body language and facial expressions, and understand the emotions behind them.

What is a Right Brain Person Like?

A right-brained person is often described as creative, intuitive, and emotionally expressive. They tend to be more spontaneous, flexible, and imaginative than their left-brained counterparts. Right-brained individuals are also good at seeing the bigger picture and making connections between seemingly unrelated concepts. They may have a wild imagination and a strong sense of empathy towards others.

Right Brain Dominance

While most people use both hemispheres of their brains equally, some individuals exhibit a greater dominance of one hemisphere over the other. Right-brain dominance means that the right hemisphere is more active and influential than the left hemisphere. According to some studies, 50% of the population may be right-brain dominant. Although most of us possess a dominant hemisphere, it is essential to note that both hemispheres are still involved in all cognitive functions.

What is a Left Brained Person Like?

Left-brained individuals are often logical, analytical, and detail-oriented. They are better at tasks that require language, math, reasoning, and organization. They thrive on facts and figures and can work methodically towards a goal. Left-brained people tend to be linear thinkers and may struggle with creativity, visualization, and holistic thinking.

Right Brain Functions

The right hemisphere of the brain plays a critical role in several cognitive functions:

Creativity – The right brain processes information in a way that allows for the generation of new ideas and concepts.

Emotion – The right brain is more active when it comes to processing emotions, including empathy and social cues.

Visual Perception – The right brain is dominant in visual and spatial perception, which enables us to interpret and navigate the world around us.

Intuition – The right brain processes information holistically, allowing for quick and instinctive decision-making.

Right Brain vs. Left Brain Test

Several tests and quizzes on the internet claim to assess whether you are right or left-brained. However, a study conducted at the University of Utah revealed that the brain patterns of right and left-brained individuals were similar, making these tests unreliable. While there may be differences in the way left and right-brained individuals process information, it is essential to note that both hemispheres work together in various cognitive tasks.

Right Brain Activities

There are several activities that can help stimulate the right hemisphere of the brain and promote creative and intuitive thinking. Here are some of our top picks:

Music – Listening to music can activate several areas of the right brain, promoting creativity and emotional expression.

Art – Engaging in artistic activities, including drawing, painting, and sculpting, can stimulate the right hemisphere of the brain and improve visual-spatial skills.

Mind Mapping – Mind mapping is a visual thinking and note-taking technique that can help improve creativity and critical thinking skills.

Meditation – Meditation is an excellent way to quiet the mind and promote intuitive thinking. It can enhance self-awareness and boost creativity.

What Does Having a Right-Sided Brain Mean?

Having a right-sided brain means that the right hemisphere of your brain is more active and influential in your cognitive functions. This dominance may lead to specific cognitive abilities, including creativity, visual-spatial skills, and emotional intelligence.

In conclusion, the right hemisphere of the brain is responsible for creativity, intuition, and emotional intelligence. While most individuals use both hemispheres of the brain equally, some exhibit a greater dominance of one hemisphere over the other. Right-brained individuals tend to be creative, intuitive, and emotionally expressive. There are several activities that can help stimulate the right hemisphere of the brain, including music, art, and meditation. However, it is essential to note that both hemispheres of the brain are involved in all cognitive functions and work together to process information.

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The Right Hemisphere Is Responsible for the Greatest Differences in Human Brain Response to High-Arousing Emotional versus Neutral Stimuli: A MEG Study

Mina kheirkhah.

1 Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20814, USA; [email protected] (J.R.G.); vog.hin.liam@cetaraz (C.A.Z.)

2 Biomagnetic Center, Jena University Hospital, 07747 Jena, Germany; [email protected]

3 Department of Psychiatry and Psychotherapy, Jena University Hospital, 07743 Jena, Germany; [email protected]

Philipp Baumbach

4 Department of Anesthesiology and Intensive Care Medicine, Jena University Hospital, 07747 Jena, Germany; [email protected]

Lutz Leistritz

5 Institute of Medical Statistics, Computer and Data Sciences, Jena University Hospital, 07740 Jena, Germany; [email protected]

Otto W. Witte

6 Hans Berger Department of Neurology, Jena University Hospital, 07747 Jena, Germany; [email protected]

Martin Walter

Jessica r. gilbert, carlos a. zarate jr., carsten m. klingner, associated data.

Studies investigating human brain response to emotional stimuli—particularly high-arousing versus neutral stimuli—have obtained inconsistent results. The present study was the first to combine magnetoencephalography (MEG) with the bootstrapping method to examine the whole brain and identify the cortical regions involved in this differential response. Seventeen healthy participants (11 females, aged 19 to 33 years; mean age, 26.9 years) were presented with high-arousing emotional (pleasant and unpleasant) and neutral pictures, and their brain responses were measured using MEG. When random resampling bootstrapping was performed for each participant, the greatest differences between high-arousing emotional and neutral stimuli during M300 (270–320 ms) were found to occur in the right temporo-parietal region. This finding was observed in response to both pleasant and unpleasant stimuli. The results, which may be more robust than previous studies because of bootstrapping and examination of the whole brain, reinforce the essential role of the right hemisphere in emotion processing.

1. Introduction

The brain’s response to emotional stimuli—and the accompanying question of whether hemispheric asymmetries exist for such responses—remains controversial despite numerous investigations [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. Studies reported variations in left and right hemisphere responses to positive and negative emotions. For instance, a left hemisphere lesion was reported to inhibit the perception of positive emotions, and unilateral right hemisphere brain damage was reported to inhibit the perception of negative emotions [ 11 ]. Some studies have reported a right hemisphere advantage for emotional face processing in patients with split-brain [ 12 , 13 ]. Evidence also suggests that happy and sad facial expressions in response to happy and sad movie clips were associated with right frontal lobe dominance [ 14 ]. Moreover, several studies reported a primary triggering of the right hemisphere for more sensitive stimuli [ 15 , 16 ].

Two main models have emerged to date which have sought to describe hemispheric lateralization in emotion processing: (1) the right hemisphere hypothesis, which posits right hemisphere dominance for all emotions, whether positive or negative [ 2 , 3 , 17 ], and (2) the valence hypothesis, which posits right hemisphere dominance for negative emotions and left hemisphere dominance for positive emotions [ 1 , 18 , 19 ]. While review studies have also examined these two hypotheses within the context of the relationship between the brain hemispheres, results have been mixed. For example, one meta-analysis of 105 functional magnetic resonance imaging (fMRI) studies (conducted from 1990 to 2008) with healthy participants and emotional faces as stimuli found no evidence for right hemisphere dominance; rather, evidence was found to support bilateral activation of emotion-related brain regions such as the amygdala, parahippocampal gyrus, and middle temporal gyrus [ 20 ]. In contrast, another review of 32 studies (conducted from 1993 to 2018 with frontotemporal lobar degeneration patients as participants) found that almost all of the examined studies supported the right hemisphere hypothesis [ 9 ]. Taken together, the existing evidence suggests that further studies investigating hemispheric specialization in emotion processing are needed.

In studies that targeted the brain’s emotional responses, results have been inconsistent—despite using the same study designs or analytical approaches. Such inconsistencies have been attributed to differences in participant groups (e.g., age), different stimuli (e.g., visual versus auditory) with different emotional categories (e.g., pleasant, unpleasant, anger, surprise, etc.), different levels of arousal, valence, and dominance (weak versus strong) within those stimuli, all of which could affect emotional responses in the human brain, and variations in study design, facilities, and analytical approaches [ 21 , 22 ]. Artificially increasing the number of samples by employing bootstrapping and random resampling can help address potential issues such as smaller sample sizes and limited stimuli presentation [ 23 , 24 , 25 , 26 , 27 ]. Such resampling methods have been used in many studies analyzing the brain’s response to emotional stimuli and have provided accurate results with high degrees of reliability [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ].

This study used bootstrapping techniques to identify the brain regions showing the highest responses to high-arousing stimuli compared to neutral stimuli. As noted above, possible outcomes included either right hemispheric dominance for both pleasant and unpleasant versus neutral stimuli or right hemispheric dominance for unpleasant stimuli and left hemispheric dominance for pleasant versus neutral stimuli. Magnetoencephalography (MEG) was chosen because it provides higher spatial resolution than electroencephalography (EEG) and higher temporal resolution than other neuroimaging technologies such as fMRI and positron emission tomography (PET) [ 37 , 38 , 39 , 40 ]. Furthermore, because many studies reported that high-arousing stimuli elicited higher activation than neutral stimuli within 200–800 ms [ 41 , 42 , 43 , 44 , 45 , 46 ], with a maximum amplitude within 270–320 ms in MEG (M300, [ 40 ]), the study also focused on this time window.

2. Materials and Methods

2.1. overview.

Figure 1 summarizes the entire algorithm of this study. First, MEG data were measured from 17 healthy participants while they viewed three categories of pictures: pleasant, unpleasant, and neutral. Second, MEG data were preprocessed separately for each participant. Third, a bootstrap approach was performed to randomly resample the data from each participant separately by calculating the difference in brain response to high-arousing emotional versus neutral stimuli. Finally, those sensors that showed the maximum differences in most replications of bootstrapping were selected as the best sensors.

Workflow of the proposed algorithm to find the MEG sensors showing greater differences in human brain response to high-arousing emotional stimuli compared to neutral stimuli.

2.2. Participants

Twenty-one healthy volunteers (12 females, aged 19 to 33 years; mean age, 27.5 years) participated in the study. Data from four participants were discarded (due to sleepiness, partial participation, or excessive movements). Data from the remaining 17 participants (11 females, aged 19 to 33 years; mean age, 26.9 years) were included in the study. Participants had no history of any neurological or psychiatric disorders and normal or corrected-to-normal vision and were not on any medications with central nervous system (CNS) effects. Informed written consent was provided by all participants before the experiment, and the details of the experiment were approved by the local Ethics Committee of the Jena University Hospital (Jena, Germany).

2.3. Stimuli and Design

One hundred and eighty color pictures were selected from the International Affective Picture System (IAPS) [ 47 ]. Sixty of the pictures were pleasant, 60 were neutral, and 60 were unpleasant. The selected pictures covered a wide range of content, e.g., happy families, household objects, sports scenes, attack scenes, etc. A description of the content and the numbers of the selected IAPS pictures are listed in Supplementary Table S1 . All 180 pictures were then divided into three blocks of 60 pictures each, comprising 20 pictures from the pleasant category, 20 pictures from the unpleasant category, and 20 pictures from the neutral category in a pseudo-randomized order.

Participants were seated in the MEG scanner in a magnetically shielded and sound-sheltered room in the Bio-magnetic Center of Jena University Hospital. Pictures were presented on a white screen in front of participants with a viewing distance of approximately 105 cm and a viewing angle of 16.5° × 21.5°; the pictures had a maximum size of 30.9 cm × 41.5 cm. Each picture was shown on the screen for 6000 ms, followed by randomized inter-trial intervals of between 2000–6000 ms; there was a brief pause between blocks to allow participants to relax. Both the contrast (as measured with ImageJ (W. Rasband, NIH, Bethesda, MD, USA)) and the mean luminance (as measured with the MATLAB 9.3.0 Lab color-space toolbox; Mathworks, Natick, MA, USA) of the selected pictures in each picture category were matched. Participants were instructed to keep their eyes open and not to move their bodies while passively viewing pictures to reduce artifacts in the MEG data. The entire MEG measurement took approximately 45 min. When the task was completed, participants took a short break and were then were shown all the pictures again in the same order (outside the MEG room) and asked to rate them using the Self-Assessment Manikin (SAM; [ 48 ]) scale. This 7-point Likert scale denotes degree of arousal (1 to 7, relaxed to excited) and valence (1 to 7, pleasant to unpleasant). The ratings were used to verify that arousal levels were significantly higher for pleasant versus neutral pictures ( p < 0.001), and unpleasant versus neutral pictures ( p < 0.001) (see Supplementary Figure S1 ).

2.4. MEG Acquisition and Processing

The study used a 306-sensor Electa Neuromag Vectorview MEG system (Elekta Neuromag Oy, Helsinki, Finland) with 204 gradiometers and 102 magnetometers (with 24-bit digitization, 1 kHz sampling rate, and online low and high-pass filter at 330 and 0.1 Hz, respectively) to measure brain activity. Only data collected from the magnetometers were analyzed in this study. A 3D digitizer (3SPACE FASTRAK, Polhemus Inc., Colchester, VT, USA) was used to define participants’ anatomical landmarks (preauricular points and nasion). MEG sensor positions for all participants were aligned by applying Maxfilter Version 2.0.21 (Elekta Neuromag Oy) to the raw MEG data using the Signal Space Separation (SSS) method [ 49 ]. One thousand millisecond pre- to 2000 ms post-stimulus onset were defined as epochs with band-pass filtering of 1–30 Hz and down-sampling to 250 Hz. Independent Component Analysis (ICA) and visual detection were used to identify electrooculogram artifacts, electrocardiogram artifacts, and excessive movements. The event-related fields (ERFs) were calculated based on artifact-free data. The entire analysis was performed using Fieldtrip [ 50 ] in MATLAB.

2.5. Statistical Analysis

To find the brain regions that showed the highest responses to high-arousing emotional compared to neutral during M300, we performed the bootstrapping approach [ 24 , 25 , 26 , 27 ] in the present study. Bootstrapping is a random resampling method that is commonly used to assess accuracy, prediction error, variance, and several other similar measures [ 24 , 25 , 26 , 27 , 28 ]. Unlike permutation tests, which are mostly used for testing, bootstrapping is mostly used to generate large sample standard errors or confidence intervals. Bootstrapping is one of the simplest techniques among the many random resampling techniques due to its benefit of being fully automatic [ 24 ]. This approach is superior to other techniques (e.g., ANOVA) when the data distribution is non-normal or even unknown and when the sample size is small [ 27 ]. The analysis of distribution properties of variables under investigation revealed that the normality assumptions for our data set were not substantiated. In combination with the small sample size, bootstrap approaches are more appropriate than asymptotic, parametric confidence interval estimators. In the present study, bootstrapping was performed on each participant’s data. We initially had 60 trials in each stimulus category (i.e., pleasant, unpleasant, and neutral), but due to the removal of artifacts in the preprocessing steps, the number of remaining trials in these stimulus categories was not equal. For example, 54 trials were left in the pleasant category, 58 in the unpleasant category, and 55 in the neutral category. Therefore, we considered the number of trials in the category with the lowest number of trials for the bootstrapping subsample (i.e., 54 in our previous example). Then this number of trials was randomly selected (with sub-sampling) from the trials in each category and averaged over the 270–320 ms time interval of interest (M300). Thus, for each category, a vector of 102 values corresponding to 102 sensors was provided. Thereafter, the vector values of the neutral category were subtracted from the vector values of the pleasant and unpleasant categories separately and the maximum of these subtractions was obtained. It should be noted again that we did not combine pleasant and unpleasant but compared them separately to the neutral responses to see if different regions and hemispheres were responsible for the positivity and negativity of the effects. In this step, the sensors with a maximum difference equal to or above the 90th percentile (largest differences) were selected. This procedure was performed for 25,000 replications ( Figure 2 ). The sensors which were above the 90th percentile in at least 20% of bootstrapping replications (orange sensors in Figure 3 ) were selected as sensors showing the highest brain responses to high-arousing emotional versus neutral stimuli. The threshold of 20% was considered because we wanted to find at least 10 sensors that showed the largest differences to see the distribution of these sensors, whether they corresponded to the same sensor locations or not. We then tested these results using the one-sample t-test to see if the selected sensors showed significantly higher responses to high-arousing emotional versus neutral stimuli. The sensors with significant p-values ( p < 0.05) are highlighted in red in Figure 3 . The total selected sensors of all bootstrapping replications for all participants were evaluated in a forest plot (separately for pleasant and unpleasant versus neutral) considering 95% confidence intervals to find out which sensors were most frequently selected for all participants ( Figure 4 ).

Selection of sensors in bootstrapping replications. The bar plots represent the sensors that expressed the highest differences in each participant’s brain response to highly arousing pleasant ( left ) and unpleasant ( right ) emotional pictures compared to neutral pictures during the M300 time interval detected in each bootstrap replication. The Y-axis indicates the 25,000 bootstrap replications. The X-axis shows the 102 magnetometers encompassing the whole brain.

Selected sensors showing the highest differences in brain responses to pleasant and unpleasant versus neutral pictures for each participant. The plots depict the magnetoencephalography (MEG) sensors across the entire head (small black circles). Highlighted sensors (in orange and red) indicate the sensors selected by bootstrapping, showing the largest differences in brain response to pleasant and unpleasant versus neutral pictures for each participant. The highlighted orange sensors are those that were selected by more than 20% of bootstrapping replications, and the red sensors are those that showed significantly higher responses to high-arousing emotional pictures versus neutral pictures within 20% of bootstrapping replications.

Forest plot for all selected sensors by bootstrapping over all participants. Vertical lines show the 95% confidence intervals for the selected sensors based on 25,000 bootstrapping replications for all participants, with the median values represented by black dots. Orange lines show the most frequently selected sensors for all participants with the highest median and the highest lower limits in confidence intervals. The bottom graphs depict the location of the selected sensors (orange lines in the top figures) which are located in the right temporal and parietal regions.

When the bootstrapping method was applied to each participant’s data ( Figure 2 ), the MEG sensors that best identified the difference in brain response to pleasant and unpleasant versus neutral stimuli were found to be mostly within sensors numbered 40–50 and 84–102 ( Figure 2 ), which were located in the right temporal and parietal regions ( Figure 3 ). Related brain regions to the selected sensors were defined based on the Elekta Neuromag sensor locations (see Supplementary Figure S2 ) [ 33 , 42 , 51 , 52 , 53 , 54 , 55 ]. For most participants, these selected sensors showed significantly ( p -value < 0.05) higher brain responses to high-arousing versus neutral pictures (red sensors in Figure 3 ). To evaluate these selected sensors by 25,000 bootstrapping replications across all participants, we plotted a forest plot showing the 95% CI of bootstrapping replications with the median across all participants ( Figure 4 ). The best sensors were selected based on the highest median value together with the highest lower limit in the confidence intervals. Finally, sensor numbers 48, 49, 84, and 91 were selected as the sensors showing the highest brain responses to unpleasant versus neutral over all participants. These sensors were selected for at least 16 out of 17 participants. Comparing brain responses to pleasant versus neutral stimuli, sensors number 41, 47, 48, 49, 50, 84, and 91 were selected as the common sensors across all participants. These sensors were common in at least 14 out of 17 participants. All of these final selected sensors for both comparisons were located in the right temporal and parietal brain regions ( Figure 4 ). Table 1 shows the details of how many of the participants showed these common sensors (repetition across participants), and in which of the participants these sensors showed the significantly higher brain responses to high-arousing versus neutral stimuli (highlighted with an asterisk). For instance, according to Table 1 , sensor number 41 was selected for 16 participants by bootstrapping replications (95% CI (2277, 10,576); median = 7143) and showed significantly higher brain responses to pleasant versus neutral stimuli in participants: 1, 4, 6, 7, 10, 12, 13, 14, 15, 16. More details on the ranges of confidence intervals and medians of the replications related to these sensors can be found in this table.

Most frequently selected sensors comparing brain responses to high-arousing emotional versus neutral pictures across all participants. The most common sensors between participants, selected considering 95% confidence intervals of bootstrapping replications, are presented in this table. In highlighted participants with an asterisk, the brain responses to high-arousing versus neutral stimuli were significantly higher. The numerical values in the labeled 95% CI column represent the median as well as the 95% CI of the bootstrapping replications for the selected sensors (see orange sensors in Figure 4 ).

* p < 0.05.

4. Discussion

This study used bootstrap methods that have not previously been used in other MEG/EEG studies to find differences in human brain response to high-arousing emotional versus neutral stimuli during the M300 time interval. The results suggest that the right hemisphere may be responsible for the largest differences in such responses, suggesting the right hemisphere may also be crucial for high-arousing emotional processing.

Our results support previous findings [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 15 , 16 , 42 , 56 ] that the right hemisphere is more involved in responding to emotion than the left hemisphere. For instance, Diamond and colleagues reported that the right hemisphere was the primary trigger and seemed to be responsible for more sensitive emotions [ 16 ], and Hecaen and Angelergues similarly demonstrated that primitive sensory data could be processed in the right hemisphere [ 15 ]. In another study, Wittling and Roschmann presented 54 adult participants with positive and negative movies to either their left or right hemisphere and found that participants reported a heightened emotional experience when either movie was shown to the right hemisphere [ 56 ]. Taken together, these findings support the right hemisphere hypothesis—that the right hemisphere is responsible for more primitive and nonverbal sensorimotor functions such as unconscious emotional processing, and that the left hemisphere is more responsible for prevalent verbal functions such as intentionality [ 3 , 4 , 5 , 6 , 7 , 8 , 9 ].

Notably, our results are in line with many animal and human neuroimaging studies that observed activation of the temporal and parietal regions in emotional and cognitive processing [ 10 , 21 , 57 , 58 , 59 , 60 , 61 , 62 , 63 ]. For instance, functional magnetic resonance (fMRI) studies have repeatedly reported higher blood oxygen level-dependent (BOLD) signals over the temporal region in response to high-arousing emotional versus neutral stimuli [ 57 , 64 , 65 ]. It should be noted, however, that other studies reported that this difference activated only the right or left temporal lobe for different types of arousal [ 51 , 57 ]. In one fMRI study, Aldhafeeri and colleagues reported bilateral activation of the temporal lobe in response to viewing pleasant versus neutral IAPS images and only right temporal lobe activation when viewing unpleasant versus neutral images [ 57 ]. In another MEG study, Hagan and colleagues reported a significant increase in the power of brain responses in the right superior and middle temporal gyrus to fear compared to neutral audio-visual stimuli [ 66 ]. In another study, Horton demonstrated high dominance of the right parietal region in response to positive emotions like joy and love [ 61 ]. Within this context, the present findings showed that the largest differences in response to high-arousing emotional versus neutral stimuli occurred in the right temporo-parietal region for most participants, regardless of whether the high-arousing stimuli were positive or negative. These findings are in line with previous studies that reported activation of the right temporal and parietal regions during high-arousing conditions such as happiness and sadness (e.g., [ 21 , 57 , 62 ]), as well as with results of a recent MEG study that reported activation of the right middle temporal gyrus during the processing of high-arousing pictures [ 67 ]. Moreover, our results are also consistent with the results of an fMRI study which tested the topography of affective states and found that the right temporo-parietal regions were essential for complexity, intensity (relates to arousal), and polarity (relates to valence) of emotional experiences [ 62 ].

It should be noted that the activity observed over the temporal and parietal regions in this study in response to high-arousing emotional stimuli may also be associated with the right amygdala and insula. For instance, a MEG study by Chen and colleagues found that activation of the right insula differentiated brain response to emotionally arousing versus neutral stimuli; in that study, the right insula was activated in response to both negative and positive stimuli [ 68 ]. However, other studies have consistently reported activation of the right insula solely in response to disgust and other negative stimuli (e.g., [ 69 ]. In addition, amygdalar activation may also be related to brain response to arousal within the 200–300 ms time interval [ 43 , 67 ]. Other studies have similarly noted higher activation of the right amygdala versus the left amygdala in response to high-arousing emotional stimuli [ 65 ] and unconscious processing of emotional stimuli [ 67 , 70 , 71 , 72 ], lending further credence to the aforementioned right hemisphere hypothesis [ 3 , 4 , 5 , 6 , 7 , 8 , 9 ].

Our study shows inline—or, in some cases, superior—results with many studies using other random resampling methods. For instance, an EEG study performed ANOVA to investigate oscillatory brain activities during the viewing of pleasant, unpleasant, and neutral pictures and found a right-hemispheric dominance of gamma oscillations for arousal stimuli [ 73 ]. Using ANOVA and permutation statistics in a MEG study, Moratti and colleagues found an arousal modulation in the right temporoparietal cortex of 15 healthy female participants [ 74 ]. In another EEG study using ANOVA, Guntekin and colleagues found higher delta coherence in the brain responses of 28 healthy subjects to unpleasant versus neutral pictures in several brain regions, including the right parietal area [ 75 ]. However, using 1000 Monte Carlo permutations with cluster correction in an EEG study, Duma and colleagues found no significant differences between the brain responses of thirty healthy participants to high versus low arousal sensory stimuli (faces or sounds) [ 76 ].

Taken together, our results reinforce the essential role of the right hemisphere in emotion processing. However, some limitations should be considered in further studies. First, the analysis performed here was based on sensor-level data; additional source-level analysis could provide complementary information. Second, the stimuli considered in this study were visual (selected from the IAPS); thus, it is worth testing whether performing the same analysis with audiovisual and audio stimuli would yield the same results. Third, consideration of other emotional categories (e.g., fear, anger, and surprise) versus neutral could also provide supporting information, rather than considering the basic emotional categories (i.e., pleasant, and unpleasant). Fourth, the arousal effect was the focus of the present study and testing our approach on the valence effect (i.e., pleasant versus unpleasant) is a proposed area for further study—in which case a different time interval should be considered, as valence and arousal are related to different stages of emotion processing [ 77 ].

5. Conclusions

The present study demonstrated that the right hemisphere may be responsible for the largest differences in brain response to both negative and positive high-arousing emotional versus neutral stimuli. In this study, we combined MEG with the bootstrapping method to identify the brain regions most likely to be responsible for these differences. Significant advantages to the study included our ability to look at the whole cortex, the use of bootstrapping methods to increase confidence intervals, and the use of MEG data, which have higher spatial resolution than EEG and higher temporal resolution than other neuroimaging technologies such as PET and fMRI.

Acknowledgments

The authors gratefully thank R. Huonker, S. Heginger and T. Radtke for technical assistance and I. Henter for editorial assistance. We also express our gratitude to the anonymous reviewers who pointed out valuable comments that improved our manuscript. The authors acknowledge BioRender and Adobe Illustrator for the use of their image-making software.

Supplementary Materials

The following are available online at https://www.mdpi.com/2076-3425/11/8/960/s1 , Figure S1: arousal and valence levels for each picture category; Table S1: numbers and descriptions of IAPS pictures used in this experiment.

Author Contributions

Conceptualization, O.W.W. and C.M.K.; Data curation, M.K. and P.B.; Formal analysis, M.K. and P.B.; Funding acquisition, O.W.W. and C.M.K.; Investigation, M.K., P.B. and C.M.K.; Methodology, M.K., P.B. and C.M.K.; Project administration, O.W.W. and C.M.K.; Resources, O.W.W. and C.M.K.; Supervision, O.W.W. and C.M.K.; Validation, M.K., L.L. and P.B.; Visualization, M.K.; Writing—original draft, M.K.; Writing—review & editing, M.K., P.B., L.L., O.W.W., M.W., J.R.G., C.A.Z. and C.M.K. All authors have read and agreed to the published version of the manuscript.

This research was funded in part by BMBF (IRESTRA 16SV7209 and Schwerpunktprogramm BU 1327/4-1) and by the Intramural Research Program at the National Institute of Mental Health, National Institutes of Health (IRP-NIMH-NIH; ZIAMH002927).

Institutional Review Board Statement

The details of the study were approved by the local Ethics Committee of the Jena University Hospital (4415-04/15), Jena, Germany.

Informed Consent Statement

Informed consent was obtained from all participants involved in the study.

Conflicts of Interest

C.A.Z. is listed as a co-inventor on a patent for the use of ketamine in major depression and suicidal ideation; as a co-inventor on a patent for the use of (2 R ,6 R )-hydroxynorketamine, ( S )-dehydronorketamine, and other stereoisomeric dehydroxylated and hydroxylated metabolites of ( R,S )-ketamine metabolites in the treatment of depression and neuropathic pain; and as a co-inventor on a patent application for the use of (2 R ,6 R )-hydroxynorketamine and (2 S ,6 S )-hydroxynorketamine in the treatment of depression, anxiety, anhedonia, suicidal ideation, and post-traumatic stress disorders. He has assigned his patent rights to the U.S. government but will share a percentage of any royalties that may be received by the government. All other authors have no conflict of interest to disclose, financial or otherwise.

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Home — Essay Samples — Nursing & Health — Human Brain — Left-Brain Versus Right-Brain Myth

Left-brain Versus Right-brain Myth

• Categories: Human Brain

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Words: 1739 |

Published: Feb 9, 2022

Words: 1739 | Pages: 4 | 9 min read

Table of contents

Origin of the myth and supporting evidence, evidence against the myth.

• Bandura, A. (1994). Self-efficacy. In V. S. Ramachaudran (Ed.), Encyclopedia of human behavior (Vol. 4, pp. 71-81). New York: Academic Press. (Reprinted in H. Friedman [Ed.], Encyclopedia of mental health. San Diego: Academic Press, 1998).
• Bruer, J. T. (2002). Avoiding the pediatrician's error: How neuroscientists can help educators (and themselves). Nature Neuroscience (Supplement), 5, 1031–1033.
• Dündar, S. and Gündüz, N. (2016), Misconceptions Regarding the Brain: The Neuromyths of Preservice Teachers. Mind, Brain, and Education, 10: 212-232. doi:10.1111/mbe.12119
• Gazzaniga, M. S. (2015). Tales from both sides of the brain: a life in neuroscience (1st ed.). New York, NY: Ecco.
• Gibson, C., Folley, B. S., & Park, S. (2009). Enhanced divergent thinking and creativity in musicians: A behavioral and near‐infrared spectroscopy study. Brain and Cognition, 69, 162–169.
• Lienhard, D. A. (2017, December 27). Roger Sperry’s split-brain experiments (1959–1968). Embryo Project Encyclopedia. Retrieved from http://embryo.asu.edu/handle/10776/13035.
• Lindell, A. K. (2006). In your right mind: Right hemisphere contributions to human language processing and production. Neuropsychology Review, 16, 131–148.
• Nielsen J.A., Zielinski B.A., Ferguson M.A., Lainhart J.E., Anderson J.S. (2013). An evaluation of the left-Brain vs. right-brain hypothesis with resting state functional connectivity magnetic resonance imaging. PLoS ONE 8(8), e71275. https://doi.org/10.1371/journal.pone.0071275
• Noggle C.A., Hall J.J. (2011) Hemispheres of the Brain, Lateralization of. In: Goldstein S., Naglieri J.A. (eds) Encyclopedia of Child Behavior and Development. Springer, Boston, MA
• Pines, M. (1973) Two astonishingly different persons inhabit our heads. The New York Times Sunday Magazine. from https://www.nytimes.com/1973/09/09/archives/we-are-leftbrained-or-rightbrained-two-astonishingly-different.html
• Reilly, J., Losh, M., Bellugi, U., & Wulfeck, B. (2004). Frog, where are you? narratives in children with specific language impairment, early focal brain injury and Williams Syndrome. Brain and Language, 88, 229–247.
• Runco, M. A. (2004). Creativity. Annual Review of Psychology, 55, 657–687.
• Society for Neuroscience (2009, June). Neuroscience Research in Education Summit: The Promise of Interdisciplinary Partnerships Between Brain Sciences and Education. University of California, Irvine. June 22–24, 2009. http://www.ndcbrain.com/articles/SocietyforNeuroscience-EducationSummitReport.pdf
• Sperry, R. W. (1961). Cerebral Organization and Behavior.  Science, 133, 1749–1757. http://people.uncw.edu/puente/sperry/sperrypapers/60s/85-1961.pdf
• Sperry, R.W. (1984). Consciousness, personal identity and the divided brain. Neuropsychologia, 22, 661-673.
• Waters, E. (2017). Waters, Elizabeth: The left brain vs. right brain myth. [Video file]. Retrieved from https://ed.ted.com/lessons/the-left-brain-vs-right-brain-myth-elizabeth waters#discussion

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• Essay #5 Yin/Yang & the Hemispheres of the Brain

“A spiral, folding within itself….”

Light and dark submerging within and emerging from out of each other…., unconscious and conscious thoughts, feelings, urges interweaving…..

The Yin/Yang symbol of the Tao, one of the most enduring in the perennial philosophy, is a great diving off point for contemplating a shift in emphasis to the right hemisphere of our brains in order to regain our emotional/psychological/spiritual balance here in the 21 st century.

Soon after choosing philosophy as my college major, I encountered this symbol for the first time while browsing in a college book store. Over 50 years later, I’m still mesmerized by both its simplicity and complexity all at once.

On the “explicate” level, it’s relatively simple:  black and white sections of a circle divided evenly by a spiral, a white dot within the black, a black dot within the white.

But the deeper “implicit” levels are what stopped me in my tracks (although I had no reason why)  and are the powerful magnetic pull that has made it one of the most enduring symbols in human evolution.

As brought up in previous essays, the left hemisphere of our brains is skilled at breaking things down into smaller parts and analyzing how they are put together (explicit).  The right hemisphere is wired to get a bigger picture or deeper “implicit” meaning which often can’t be best explained in words, but understood at an intuitively felt level.

A common phrase used to define what the yin/yang symbol represents is “Unity of opposites.”  On the explicate level, the black and white sections can be perceived as two opposing forces.  On the implicate level, according to many Taoist accounts, the opposing forces are generated from an underlying, unseen unity/harmony.

So, at the explicate level, yin/yang can reflect a constant pattern of conflict, opposition and competition. From the perspective of the right hemisphere, as taught through the millennia by more intuitive philosophers and spiritual sages, the spiral within the circle reflects a continuous flow between the black and the white which co-exist in an underlying harmony.

Diving into the Spiraling Wave

As with many explorations of ancient Asian wisdom, I turn to one of the most gifted teachers at evoking this wisdom and applying it to our modern age:  Alan Watts .

He once stated:

“The yin/yang symbol is a spiral folding within itself.”

With this perspective, let’s dive in.

Often a good place to start when exercising right hemisphere modes of perception is a teaching tale.  Here is one of the most famous Taoist stories, as written in Alan Watts’ book Tao:  The Watercourse Way :

“There was a farmer whose horse ran away. That evening the neighbors gathered to commiserate with him since this was such bad luck. He said, “May be.” The next day the horse returned, but brought with it six wild horses, and the neighbors came exclaiming at his good fortune. He said, “May be.” And then, the following day, his son tried to saddle and ride one of the wild horses, was thrown, and broke his leg. Again, the neighbors came to offer their sympathy for the misfortune. He said, “May be.” The day after that, conscription officers came to the village to seize young men for the army, but because of the broken leg the farmer’s son was rejected. When the neighbors came in to say how fortunately everything had turned out, he said, “May be.”   

You can hear Alan Watts talking about yin/yang here.

He comments on the fact that the symbol contains a white dot in the black pattern and a black dot in the white pattern:

“Obviously black and white are as different as different can be…but strangely black is white in a strange sense. And white is black…because black implies white and white implies black. All positive implies negative and negative implies positive. Because you can’t have the one without the other. To put this into clear words we can say explicatively, black and white are different. But implicitly…they are one. So outwardly, the positive and negative of life are very different.  Life is different from death and good is different from evil. But esoterically, secretively, they are one.” “Thus, rather than seeing nature as a conquest between opposing forces, the cold vs the heat, the light vs the dark, the day vs the night, man vs woman, the principle of the Yin-Yang is that of mutually-arising. That is to say, to adopt an organic view of nature and appreciate the underlying unity behind the apparent duality. To demonstrate cooperation and harmony in all the various phenomena of nature.”

Nature’s Expression of Yin/Yang

Contemplating down to an individual atom, the building block of nature, we find the unity underlying the apparent opposition: Each atom contains a proton with a positive charge and electrons with negative charge.

At its core, nature generates symmetry through opposites attracting and like repelling.

In the plant world, we easily get entranced by the beauty of the flowers and the trunk, branches and leaves of a tree reaching up towards the sunlight. But that is only half the story.

As beautiful as these photos are, they leave out ½ of the whole picture…As if being captivated by the white section of the yin/yang symbol, being blind to the dark section.

The missing part?  The roots pushing deep into the dark muck of the earth for sustenance, without which the trees we see in the above photographs couldn’t exist, a vivid example of the “explicit” (left hemisphere) being overemphasized to such a degree that the “implicit” roots of life are forgotten.

And science is now telling us that at the “root” level, trees communicate with each in life-enhancing ways. As described in the article published by Smithsonian Magazine, “Do Trees Talk to Each Other?” based on observations by German forester Peter Wohlleben,

“A revolution has been taking place in the scientific understanding of trees, and Wohlleben is the first writer to convey its amazements to a general audience. The latest scientific studies, conducted at well-respected universities in Germany and around the world, confirm what he has long suspected from close observation in this forest: Trees are far more alert, social, sophisticated—and even intelligent—than we thought…”

The article goes on to confirm a significant understanding of evolution:

“Since Darwin, we have generally thought of trees as striving, disconnected loners, competing for water, nutrients and sunlight, with the winners shading out the losers and sucking them dry. The timber industry in particular sees forests as wood-producing systems and battlegrounds for survival of the fittest. There is now a substantial body of scientific evidence that refutes that idea. It shows instead that trees of the same species are communal…These soaring columns of living wood draw the eye upward to their outspreading crowns, but the real action is taking place underground, just a few inches below our feet. “Some are calling it the ‘wood-wide web,’ says Wohlleben.”

The “wood-wide web” clearly includes both underground at the root level as well above ground.

At the same time evidence such as the “wood-wide web,” as detailed in the Smithsonian Magazine article, reveals nature is much more collaborative than competitive, culturally we are still stuck in the constrained paradigm that evolution is based on a ‘survival of the fittest’ based on material gains and competition. The yin/yang symbol reflects the need for collaborative harmony, not getting stuck in the explicate at the cost of missing the implicate.

Wave Theory

At the deep, implicit level of what many ancient Asian sages were tuned into, Yin and Yang, dark and light, can’t be well understood taken separately.  As Alan Watts pointed out, the spiral which visually separates them in the symbol is “folding in on itself.”  So, if we imagine the symbol in motion, the black and white sections would be submerging into and emerging out of each other, understandable only as a ‘mutual whole.’

There is another powerful example we’ve all shared that can tune into a deeper understanding of this underlying ‘mutual whole’………. Watching waves rise and fall as they approach the shoreline.

On the visual, explicit level, we can distinguish one wave from another as they rise out of the surface.  Each wave is clearly separate from the others.  But are they?

It’s virtually impossible to accurately measure where an individual wave begins and ends. For at the moment of the measurement, the wave has shifted its position from the ocean out of which it emerges.  And while at the explicit level, we can see general dimensions as the wave rises and falls, did the visual wave ever fully separate itself from the ocean as a whole?

It can’t.  For beneath the surface of the water each wave is being shaped and formed by the underlying tidal forces not just locally, but throughout the entire undersea tidal dynamics of the ocean at large.

So, at the same time a surfer can choose to ride one particular wave over another and we can distinguish each wave from others, in reality each wave is intricately woven into the expansive push/pull currents of the entire ocean.

The importance of understanding the deeper dynamic of wave/ocean is noted by Alan Watts:

“This (the yin/yang symbol) implies that the art of life is more like navigation than warfare, for what is important is to understand the winds, the tides, the currents, the seasons, and the principles of growth and decay, so that one’s actions may use them and not fight them. At the very roots of ancient Chinese thinking and feeling there lies the principle of polarity, which is not to be confused with the ideas of opposition or conflict. In the metaphors of other cultures, light is at war with darkness, life with death, good with evil, and the positive with the negative, and thus an idealism to cultivate the former and be rid of the latter flourishes throughout much of the world.”

Riding the Quantum Wave

As previously mentioned, the ancient yin/yang symbol is one of the keystones of the perennial philosophy, those transcendent insights that continue to spark the continuing search for deep, edifying patterns of existence.  While primarily an insight in philosophy and spiritual teachings, the yin/yang symbol has influenced science as well.

Niels Bohr, the Nobel Prize-winning scientist whose institute in Copenhagen was the main center for development of quantum physics, was offered a Danish knighthood in 1947. One of the perks was the opportunity to construct a personal coat of arms.  Bohr chose as its central image:  The yin/yang symbol.

This is quite interesting to our topic since it was Bohr who created the most enduring philosophical interpretation of the mysterious contradictions inherent in quantum physics.  Despite the fact that quantum physics is the most successful scientific theory ever (responsible for the current computer driven digital age), at its core, confirmed by multiple experiments, is the bizarre mystery that at the subatomic level an entity such as a photon (which makes up light) or an electron (which makes up electricity)  can be either a particle or a wave, depending on how the experiment is set up.

This makes no logical sense.  A particle has finite, discernible boundaries–a wave is diffused and has no clear boundaries.  How could anything be neither definitively one or the other, but potentially either one?

As physicist David Harrison describes the mystery of Wave/particle duality and Bohr’s philosophical vision called “complementarity:” 

“We can think of an electron as a wave or we can think of an electron as a particle, but we cannot think of it as both at once. But in some sense the electron is both at once. Being able to think of these two viewpoints at once is in some sense being able to understand Quantum Mechanics.”

To think of “two viewpoints at once” connects beautifully to Buddhist teacher Robert Thurman’s statement, cited previously on this website:

“Wisdom is tolerance of cognitive dissonance.”  

In other words, by holding the opposing viewpoints of Wave/particle duality, or for that matter, the dark and light characteristics of yin/yang in the mind, rather than choosing or defaulting to one or the another, we get a fuller sense of how life operates.

No wonder one of the greatest scientists of the 20 th century, Niels Bohr, chose the yin/yang symbol for his coat of arms honor. He was adopting the symbols inherent call:  To understand that what appear to be opposing forces (Wave/particle duality) are, at the deeper level of reality, reflections of an unseen, unified flow.

Note:  During the development of quantum physics, its most brilliant creators, Bohr, Einstein, Heisenberg, Schrodinger, Dirac, Planck, et al, devoted energetic conversation to the mysterious, esoteric philosophical revelations of the quantum world as well as the practical, observable, provable results.  But as is all too common in the Western mind by the 1950’s, the next generation of quantum physicists consciously discarded philosophizing about the deeper meaning of quantum reality (right-hemisphere) to focus entirely on achieving practical advances in quantum technology (left-hemisphere).  This left-hemisphere mind-set to forget about deep meaning and focus on practical results was captured in a quote attributed to physicist David Mermin, which became the operating mantra:

“Shut Up and Calculate!”

(The right-hemisphere might counter with ‘Open Up and Contemplate.’)

While admiring and enjoying the benefits of this left-hemisphere focus (personal computers, laser medical devices, smartphones), we can at the same time point to the crucial human need for deeper meaning and existential insight. (Fortunately, this has always re-surfaced on occasion, examples being Fritz Capra’s brilliant integration of quantum physics and ancient Asian mysticism, “The Tao of Physics” , Quantum physicist David Bohm, Einstein’s protégé, whose contemplation of underlying  unity inspired his 1980  book “Wholeness and the Implicate Order”  and, in the 21 st century, the Nobel-Prize winning theoretical physicist Frank Wilczek who wrote:

“ My 10th key to reality, which emerges from but in some ways transcends science, turned out to be ‘Complementarity is Mind-Expanding.’ Complementarity is an attitude toward life that I’ve found eye-opening and extremely helpful. It has, literally, changed my mind. Through it, I’ve become larger: more open to imagination, and more tolerant.”

Brain Patterns & Flow

We’ve all been in that wonderful, great-feeling, highly productive brain state of “flow,” where linear time seems to disappear and we move effortlessly towards a successful goal.  It’s been commented on by artists, athletes, writers, scientists, musicians and business leaders.

The ancient “spiraling within itself” image of yin and yang clearly reflect a flow inherent in the world and now modern science can explain some of flow’s origins in our brains.

An article on Peak Performance published in TIME Magazine stated,

“Over the past decade, scientists have made enormous progress on flow. Advancements in brain imaging technologies have allowed us to apply serious metrics where once was only subjective experience…

The state emerges from a radical alteration in normal brain function. In flow, as attention heightens, the slower and energy-expensive extrinsic system (conscious processing) is swapped out for the far faster and more efficient processing of the subconscious, intrinsic system.”

The quoted material above is packed with interesting allusions to right-hemisphere wiring:

• On the one hand, it points to “being in flow” as requiring a shift from “extrinsic system” qualities more associated with left-hemisphere thinking towards the “processing of the subconscious, intrinsic system,” more associated with right-hemisphere thinking.
• When we are ‘in the flow state’ our brain doesn’t slow down to break down and analyze different strategies (left-hemisphere characteristic). As the article states, when we are “in flow, the result is liberation [from second guessing]. We act without hesitation. Creativity becomes more free-flowing, risk taking becomes less frightening, and the combination lets us flow at a far faster clip” (right-hemisphere characteristics).

The article then describes the shift in brain wave states which induce this experience:

“In flow, we shift from the fast-moving beta wave of waking consciousness down to the far slower borderline between alpha and theta. Alpha is day-dreaming mode—when we slip from idea to idea without much internal resistance. Theta, meanwhile, only shows up during REM or just before we fall asleep, in that hypnogogic gap where ideas combine in truly radical ways.”

The “day dreaming” alpha wave mode and even deeper theta wave mode are much more effectively processed by the right hemisphere’s openness to totally novel, boundary-shaking messages from the subconscious than the left hemisphere’s predilection for more objective, familiar language.

(Note: As for the even deeper theta brain wave state, I address this in the next Essay:  The Creative Power of Dreams)

As Dr. Iain McGilchrist writes in “The Master and his Emissary:  The Divided Brain and the Making of the Western World,”

the book which is a major influence on this Right Brain Network website:

“ So, the left hemisphere needs certainty and needs to be right. The right hemisphere makes it possible to hold several ambiguous possibilities in suspension together without premature closure on one outcome.” 

This insight is connected on a deep level to Robert Thurman’s, previously mentioned:

“Wisdom is the tolerance of cognitive dissonance.”

Note: Robert Thurman and Iain McGilchrist were the first two guests on our webinar series “What Are We Thinking?  A Trip into the Right Hemisphere of the Human Brain.”

As we encounter the challenge of the sped up, digitalized, globalized, network-connected 21 st century, slowing down our brain waves from the hyperactive beta state to the more reflective, intuitive, open-minded right-hemisphere feels like a much-needed shift.

And if we see the yin/yang symbol as a metaphor for our brain, it can be imagined as pointing to the need for whole-brain thinking, with the two hemispheres working more in concert.  Given the well-researched, well thought-out premise of Iain McGilchrist’s “The Master and his Emissary:  “The Divided Brain and the Making of the Western World:” Western culture has been dominated for centuries by the overly self-assured, technologically oriented left hemisphere, then to achieve whole brain thinking requires a re-balancing shift to a more right hemisphere perception of the deep, powerful patterns of change occurring under the surface of the anxiety-producing 24-hour news cycle.

The yin/yang symbol, apparent oppositions folding in and out of one another, reflecting an implicit Flow & Unity underneath, is much more capable of being felt and understood in the right-hemisphere of our brains’ ability to tune into the alpha and theta brain wave frequencies, to intuit the Whole and not just the parts, to understand collaboration has a greater presence in nature than does competition, to see beyond materialism to the deeper, more pervasive non-material pattern of existence.

Enjoy exploring this week’s quotes and links:

“At heart, science is the quest for awesome – the literal awe that you feel when you understand something profound for the first time. It’s a feeling we are all born with, although it often gets lost as we grow up and more mundane concerns take over our lives.”

― Sean Carroll,  Theoretical Physicist

“The materialistic consciousness of our culture … is the root cause of the global crisis; it is not our business ethics, our politics or even our personal lifestyles. These are symptoms of a deeper underlying problem. Our whole civilization is unsustainable. And the reason that it is unsustainable is that our value system, the consciousness with which we approach the world, is an unsustainable mode of consciousness.”

―  Peter Russell, author, “The Global Brain”

“Dialogue is a space where we may see the assumptions which lay beneath the surface of our thoughts, assumptions which drive us, assumptions around which we build organizations, create economies, form nations and religions. These assumptions become habitual, mental habits that drive us, confuse us and prevent our responding intelligently to the challenges we face every day. “

— David Bohm, Quantum Physicist/Philosopher

• Essay #8: The Creative Power of Dreams
• Essay #7: Global Brain Emerging?
• Essay #6: Gaia Vision
• Essay #4: Where is Evolution Pointing its Finger?
• Essay #3: What’s the Story?
• Essay #2: Synaptic Jumps / Quantum Leaps?
• Essay #1: Signs of the Next Renaissance?
• Right Brain Links of Interest
• Mission Statement

Role of the Right Hemisphere in the Processing of Language Essay

Introduction, lateralisation and neuroscience, language patterns and psychology, technology and study, concluding remarks.

Language is a process of the right hemisphere of the brain. Physical and psychological studies have revealed much in this area, however many studies are still attempting to better understand the questions left to be explained.

In the human brain, a longitudinal fissure effectively divides the brain into two separate parts. These parts, joined by the corpus callosum, are naturally similar to each other while the structure of each half is effectively mimicked by the other side. While it would appear that there is a ‘mirroring’ or some inverse reflection between processes, the functions of each half are different. Psychology usually will create larger and more general explanations that must take care not to be labelled as pseudoscience.

However, acclaimed scientific research has supported many elements of the psychological assumptions, ranging from differences in the makeup of nerve components and the distribution of neurotransmitters. One part of the brain, the lateral sulcus, is generally larger in the left hemisphere, though the reason cannot be determined with any certainty. The degree to which brain function is assigned or specialized within certain areas of the brain is generally still the subject of research. Injuries have been found to impair specific mental processes, while sometimes nearby regions or the opposite hemisphere have been found to attempt to resume the lost functionality.

While the functions of the brain are lateralized, the lateralization’s themselves change between different brains for any given function. They also differ across specific functions in any given brain. With regards to the popular notion of people either being ‘left-brained’ or ‘right-brained,’ this is a poor way to classify the brain as people use both parts. Dominance in one hemisphere or the other but is not evident in the popularized way.

This has been found across people who prefer certain hands, certain ears when listening, although even this is not a clear definition of dominance for any hemisphere. While 95 percent of people preferring to use their right hand have a dominant left-hemisphere in the area of language, approximately 19 percent of people preferring their left hand have a dominant right hemisphere regarding language, while furthermore nearly 20 percent of the left-handed individuals were found to have bilateral language functions (Taylor et al, 1990).

This suggests that within the spectrum of components essential to the category of language, such as syntax and semantics, the level of dominance and area of the brain responsible for not only the general category may differ as well as the specifics associated within that category. It is interesting to note here that while language is normally defined by the human mind to have subareas such as language, semantics, and word choice, the activities of the brain do not show such a top-down categorization as far as location or other apparent aspects.

Neuroscience helps people to understand the power of the brain and why it how it works, while this is essential in understanding how language works in the right hemisphere. Specific branches of psychology aid in furthering theory and scientific development in this field, and are thus critically important in the same essential understanding. While psychology has been referred to as a pseudoscience in some situations, there is evidence of reciprocation in the studies of each field while each considers the findings of the other.

Research in cognitive neuroscience provides the most significant findings for the role of the right hemisphere and language, although unfortunately at this point it can be best analysed through the study of damage rather than the study of active processes. This is not to say that studying the brain activity of undamaged brains is not useful by any means, however, technology has not been able to draw the same level of specific conclusions as it has been able to in evaluating the level of brain damage in patients.

Language patterns have been related to the brain through a variety of studies in psychology, while this information must be analysed and processed in a specific manner in order to avoid being labelled pseudoscience rather than science. Many attempts have been made to understand the underlying reasons for many aspects of language, and to what extent the brain plays a role in the related subtopics. While brain damage has been known to directly affect behavioural patterns in addition to language, this relationship can be studied in an attempt to repair specific damage in an attempt to restore functional aspects of modifying behaviour as well (Frith, 2005).

The name given to the branch of this area is cognitive neuropsychology, and this field brings further understanding to the role the brain has on behaviour while allowing also for a better understanding of the physical brain. This is important to language and the right hemisphere and the fundamentals of cognitive neuropsychology are used in applications of relevant research. Cognitive neuropsychology is one of the most important fields of study in psychology generally because its applications are direct, while the understanding of the brain which results is with regards to tangible and functional aspects, rather than the more subjective loosely diagnosed disorders of clinical and other forms of psychology.

This is especially important in the foundation of continued research because cognitive neuroscience, the branch of cognitive neuropsychology which makes the most direct applications to the physical brain, could not be possible without the studies of neuropsychology. While cognitive neuroscience requires the studies of cognitive neuropsychology, cognitive neuropsychology is a subcategory of cognitive psychology.

Thus, the most critical category as far as research and development to understand the real processes of the human mind can be argued to be cognitive neuropsychology (Humphreys and Riddoch, M., 1994). The understanding of mental abilities, mental development, and behaviour as a result of the functionality of the brain makes cognitive neuropsychology one of the most scientifically relevant topics in building a knowledge base for humanity.

These applications are then used to further cognitive science which then makes the extensions upon medical science which allow people to understand the human mind in scientific regards of physical processes rather than only theorized processes (Coltheart, 2002). As such this entire process is essential in finding the real relationships, rather than any imagined or otherwise not-verifiable ones, to make scientific physiological advances in the area of psychology rather than pseudoscientific ones (Kandel, 2000).

Advancing technology has allowed for increasingly well-performed studies to take place in all areas. Regarding this case, an area of recent interest is computational cognitive neuropsychology, which is based on computerized models for cognition. With this analysts can take a more hands-on approach to analyse the roles of the right hemisphere and language. These models are computer programs that can perform certain cognitive actions including reading out loud, spelling, and other related functions of language (Dehaene, 2005). These models attempt to best emulate the human processes which occur within the brain.

The model can be further analysed in an attempt to gain real information by damaging it in certain ways while also making relations to actual brain damages. Of course, precision is required within the computer programs for the effects and information to be entirely relevant, however as this technology exists increasing emphasis and effort is going into this type of analysis and research in all brain functions (Coltheart, 2002; Toga, 2003).

The conclusions from research on patients with brain damage compared to those without it reveal that the processes involved in language are complimented across processes in each hemisphere. The right side has been found to best interpret visual meanings of specific letters of a language while the left side has been found to respectively recognizing sequences according to the rules of the language. Some studies suggest that the right hemisphere plays more of a role in the processing of language and semantics than it does in other areas (Taylor and Regard, 2003).

This split in the functions with regards to language reflects the levels of complexity and improvisation that are so evident in the nature of most languages. The left hemisphere’s short or long-term impairments have been found to free the same inhibitions on the other side. This type of research suggests that the language potential may reach much farther than previously thought with regards to semantic aspects while the functions commonly thought to be dominated by the left hemisphere may also in fact be included in the potential of the right hemisphere of the brain (Taylor and Regard, 2003).

Overall, while it is apparent that significant progress has been made in analysing the functions of the hemispheres in general, only relationships have been found while many strong conclusions remain to be made. Regarding language, psychological and physiological studies have only shown so much, and this is limited to the activities in both hemispheres in relation to many aspects of language which differ across brains and making clear classifications all the more difficult.

Theoretically, the main objective in this area of research is to clearly define the processes between the right and left hemispheres as they conduct the variety of processes associated with language. This objective is central to theory in the processing of language as well as to the understanding of lateralization, and as such, the objective can be fairly considered as being not reached nor likely reached soon. The most promising aspects of research in the future will likely stem from the study and recovery of a variety of brain-damaged patients, while computer modelling and developing technology will slowly enable better perception and analysis of active processes.

It seems quite safe to say that the right hemisphere plays more of a role in language than the left side, despite the findings that each hemisphere has the potential to perform a process. As such it is debatable whether any study will ever be able to clearly define to what extent any person’s right hemisphere may have in language processes. Research suggests that this varies to such an extent that the relationships and locations of processes in the brain may even be dependent on that person’s unique perspective and interactions with the environment.

Coltheart, M. (2002). Cognitive neuropsychology . John Wiley & Sons.

Decety, J. (1999). Perception and Action: Recent Advances in Cognitive Neuropsychology. Psychology Press .

Dehaene et al (2005). Sources of mathematical thinking: behavioural and brain-imaging evidence . Science .

Frith, C. (1995). Cognitive Neuropsychology of schizophrenia. Psychology Press .

Humphreys, G. and Riddoch, M. (1994). Cognitive Neuropsychology and Cognitive Rehabilitation . London: Lawrence Erlbaum.

Kandel E, Schwartz J, Jessel T. (2000). Principles of Neural Science . New York: McGraw-Hill.

Taylor et al. (1990) Psycholinguistics: Learning and Using Language. Neuroscience .

Taylor, K. and Regard, M. (2003). Language in the Right Cerebral Hemisphere: Contributions from Reading Studies. News in Physiological Sciences .

Toga AW, Thompson PM. (2003). Mapping brain asymmetry. Nat Rev Neuroscience .

Whitworth, A. et al (2005). A Cognitive Neuropsychological Approach to Assessment and Intervention in Aphasia. Hove: Psychology Press .

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IvyPanda. (2021, November 15). Role of the Right Hemisphere in the Processing of Language. https://ivypanda.com/essays/role-of-the-right-hemisphere-in-the-processing-of-language/

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Bibliography

IvyPanda . "Role of the Right Hemisphere in the Processing of Language." November 15, 2021. https://ivypanda.com/essays/role-of-the-right-hemisphere-in-the-processing-of-language/.

• Goals of Cognitive Neuropsychology
• Metacognition and Neuropsychology
• Contemporary Neuroimaging and Methods in Adult Neuropsychology
• Biopsychology and Its Six Major Divisions
• Dimensions of Psychology and Its Specialty Areas
• Biopsychology: Basic Precepts and Connected Fields
• Cross-Cultural Psychology in Contemporary Psychiatry
• The Two Hemispheres of the Brain
• Biological Psychology: Development and Theories
• The Hemispheres Adaptability to Function Independently
• A Passion Flower: Properties and Story of Discovery
• Lifespan Development: Adolescent Psychology
• Effect of Certain Plant Growth Retardant Hormones on “Gladiator” Pumpkin Plant Height
• Meiosis and Splitting of the Dna Into Gametes
• Anatomy Lab: Human Body Organ Systems

Right Brain May Control Writing in Some Lefties, Study Shows

• by Andy Fell
• November 18, 1996

Media Resources

Andy Fell, Research news (emphasis: biological and physical sciences, and engineering), 530-752-4533, [email protected]

Watch the Skies

When and How to Spot the ‘Devil Comet’

Comet 12P/Pons-Brooks is one of the brightest known periodic comets . It earned the nickname of “devil comet” in 2023 when an outburst caused the comet to have an asymmetrical appearance, like having horns. It comes around every 71 years and is currently getting brighter as it flies toward the Sun.

In the Northern Hemisphere, the comet is best viewed with binoculars or a small telescope – right after the Sun dips below the horizon, look West just beneath the Moon, and just right of Jupiter. An hour after sunset, the comet drops so low, it will be difficult to see without a perfectly clear view of the horizon. The comet then sets an hour later.

Bill Cooke, who leads the Meteoroid Environment Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama, encourages viewers to have more realistic expectations about what they might see. “Many images depict a bright comet with a long green tail,” Cooke said. “That’s not going to happen.”

By July, it will be too dim to view even with binoculars.

As for viewing this comet with the naked eye, it might be possible in the coming days, but by mid-April, it will be too close to the Sun and then growing fainter as it makes its way away from the Sun.

The brightest stars are a magnitude 1, the faintest are a magnitude 6. Comet 12P will peak around a magnitude 5 unless an outburst occurs.

However, Cooke warns that outbursts are unpredictable. “There have been minor outbursts roughly once a month but it’s impossible to predict them,” he said. “The last one was on Leap Day, Feb. 29.”

Will the comet be visible during the eclipse ?

It is certainly a possibility. If Comet 12P remains around a magnitude 5, it would only be visible in binoculars during the few minutes of totality. Consider enjoying the main spectacle instead of using that time to locate Comet 12P and attempt to view it at another time.

For more skywatching highlights in April, check out Jet Propulsion Lab’s What’s Up series.

By Lauren Perkins NASA’s Marshall Space Flight Center

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Cincinnati's next total solar eclipse. Start planning for 3046

On April 8, the moon will slide between Earth and the sun to make a solar eclipse. And for many people at the right place and time in Mexico, the United States and Canada, they will experience the greatest show in the universe, a total solar eclipse.

The moon’s shadow will sweep across the United States at around 2,000 miles per hour. It will travel from Dallas to Cleveland in 33 minutes.

This alignment between the sun, moon and Earth is so rare that, on average, any one spot in the northern hemisphere experiences a total solar eclipse every 330 years. But for places like Cincinnati, which has not had a total solar eclipse since 1395, this is a once in a millennium astronomical event. Especially when you consider that Cincinnati proper still won't see full totality until the year 3046.

So continue reading to figure out where to go (and when) to experience this rare totality.

Cincinnati partial solar eclipse timeline

In the city of Cincinnati and Northern Kentucky, there will not be a total solar eclipse. Many places in the area will experience 98-99% of the sun blocked by the moon. Although the sky will likely darken and the temperature will drop a little, people outside the path of totality will not experience the full dazzling effects of the total solar eclipse.

• Partial eclipse begins: 1:52 p.m.
• Maximum eclipse: 3:09-3:10 p.m.
• Partial eclipse ends: 4:24 p.m.

Find eclipse totality near you

The narrow path of totality looks like a ribbon arcing through Texas, Arkansas, Missouri, Illinois, Indiana, Ohio, Pennsylvania, New York, Vermont and Maine. The closer you are to the path of totality, the greater your partial eclipse will be. But getting into totality should be your ultimate goal.

With many schools and businesses in Cincinnati closed for the eclipse, here are nearby locations to view various amounts of totality.

• Downtown Cincinnati: 0:00 (no totality at all).
• Jungle Jim's, Fairfield: 35 seconds.
• Harrison, Ohio: 1 minute, 30 seconds.
• Hamilton, Ohio: 1 minute, 41 seconds.
• Middletown, Ohio: 1 minute, 57 seconds.
• Dayton, Ohio: 2 minutes, 42 seconds.
• Oxford, Ohio: 2 minutes, 50 seconds.
• Batesville, Indiana: 2 minutes, 59 seconds.
• Richmond, Indiana: 3 minutes, 49 seconds.
• Wapakoneta, Ohio: 3 minutes, 57 seconds.

Here's what the total solar eclipse will look like

The solar eclipse begins when the leading edge of the moon appears in silhouette in front of the sun. For most locations in the United States, the moon will first cover the bottom right section of the sun and appear to slowly move up and to the left. This is called the partial solar eclipse stage. The moon will continue to cover more of the sun over the next hour, slowly building toward the total eclipse.

During the partial eclipse stages, if even a slim crescent of sunlight is shining, you need to use certified safe solar viewing methods like eclipse glasses. Even 1% of the sun shining around the moon could still cause eye damage.

Just before totality, the last rays of sunlight trickle around the mountains of the moon. The dazzling effect is called the diamond ring because you can see the outline of the moon in front of a ghostly white light.

Solar activity has ramped up lately and you may be able to see solar prominences. These extreme eruptions on the sun, if large enough, may be visible as tiny pink protuberances peaking around the edge of the moon.

Then, at totality, the wispy, ethereal tendrils of the corona of the sun extend in various directions. While the moon is completely covering the sun, that is the only time when the sky is dark enough for you to see this outer atmosphere of the sun.

For people with specially filtered binoculars or telescopes, you can zoom in seconds before or after totality to witness Bailey's Beads: the beads of sunlight coming through the valleys and around the mountains of the moon.

Annular vs. total solar eclipses

For totality to take place, everything must be lined up perfectly. The moon, at around 240,000 miles from Earth, must move directly in front of the sun, which is 93,000,000 miles away. But the moon varies its distance from us. When it is farther from Earth, it does not appear large enough in the sky to block out the entire sun. This is called an annular solar eclipse or ring of fire eclipse since the moon appears to be nestled completely inside the disc of the sun with a ring of bright sunlight surrounding it. This last happened on Oct. 14, 2023.

In order to create a total solar eclipse, the moon must be close enough to the Earth to block out the entire sun. And even under the most perfect alignment, the moon’s shadow barely reaches the Earth’s surface to be visible along a swath of the planet 80-120 miles wide. This is called the path of totality. The maximum amount of time that the moon can totally eclipse the sun is 7 1/2 minutes, while the eclipse on April 8 will last one second at the edge of the shadow to a maximum of 4 minutes, 28 seconds in Mexico.

Don’t miss it: Next total solar eclipses by state

• Ohio: Sept. 14, 2099.
• Kentucky: Oct. 17, 2153.
• Indiana: Sept. 14, 2099.
• Texas: May 11, 2078.
• Arkansas: Aug. 12, 2045.
• Missouri: Aug. 12, 2045.
• Illinois: Sept. 14, 2099.
• Pennsylvania: May 1, 2079.
• New York: May 1, 2079.
• Vermont: May 1, 2079.
• New Hampshire: May 1, 2079.
• Maine: May 1, 2079.

Dean Regas is an astronomer, host of the Looking Up podcast, and author of six books including "100 Things to See in the Night Sky." He can be reached at astrodean.com

Eclipse Chasing : Online Astronomy Class

What: The total solar eclipse is coming Monday, April 8, and you do not want to miss it! Astronomy expert and eclipse chaser, Dean Regas, shares his tips on where to go, what to look for, and how to view it safely. Plus, he will give you tools to watch the weather forecast to make sure you go to a place with clear skies.

When: Recorded April 4, your ticket allows you to watch the class at your convenience.

Tickets: $10 per household.

Register : astrodean.com/shop .

Strong Taiwan Quake Kills 9, Injures Hundreds

The earthquake was the most powerful to hit the island in 25 years. Dozens of people remained trapped, and many buildings were damaged, with the worst centered in the city of Hualien.

• Share full article

• Hualien, Taiwan A landslide after the quake. Lam Yik Fei for The New York Times
• New Taipei City, Taiwan Books flew off shelves as a home shook. @Abalamindo via Storyful
• Taipei, Taiwan Passengers waiting at a train station as some services were suspended. Chiang Ying-Ying/Associated Press
• Hualien, Taiwan People are rescued from a building that had partially collapsed. TVBS via Associated Press
• Hualien, Taiwan Firefighters rescuing trapped residents from a building. CTI News via Reuters
• Taipei, Taiwan Students evacuated to a school courtyard after the earthquake. Lam Yik Fei for The New York Times
• Guishan Island, Taiwan Rocks tumbling down one side of an island popular for hiking. Lavine Lin via Reuters
• Hualien, Taiwan A building leaned to one side after the quake. Randy Yang via Associated Press
• Ishigaki, Okinawa, Japan Watching news on a rooftop of a hotel after a tsunami warning. Chang W. Lee/The New York Times
• Hualien, Taiwan Motorbikes damaged in the quake. TVBS via Associated Press
• New Taipei City, Taiwan Damage in an apartment Fabian Hamacher/Reuters
• New Taipei City, Taiwan Water cascading down a building during the quake. Wang via Reuters

Meaghan Tobin and Victoria Kim

Here’s what you need to know about the earthquake.

Taiwan was rocked Wednesday morning by the island’s strongest earthquake in a quarter century, a magnitude 7.4 tremor that killed at least nine people, injured more than 800 others and trapped dozens of people.

The heaviest damage was in Hualien County on the island’s east coast, a sleepy, scenic area prone to earthquakes. Footage from the aftermath showed a 10-story building there partially collapsed and leaning heavily to one side, from which residents emerged through windows and climbed down ladders, assisted by rescuers. Three hikers were killed after being hit by falling rocks on a hiking trail in Taroko National Park, according to the county government.

By late afternoon, officials said rescue efforts were underway to try to rescue 127 people who were trapped, many of them on hiking trails in Hualien.

One building in Changhua County, on the island’s west coast, collapsed entirely. The quake was felt throughout Taiwan and set off at least nine landslides, sending rocks tumbling onto Suhua Highway in Hualien, according to local media reports. Rail services were halted at one point across the island.

The earthquake, with an epicenter off Taiwan’s east coast, struck during the morning commute, shortly before 8 a.m. Taiwanese authorities said by 3 p.m., more than 100 aftershocks, many of them stronger than magnitude 5, had rumbled through the area.

In the capital, Taipei, buildings shook for over a minute from the initial quake. Taiwan is at the intersection of the Philippine Sea tectonic plate and the Eurasian plate, making it vulnerable to seismic activity. Hualien sits on multiple active faults, and 17 people died in a quake there in 2018.

Here is the latest:

The earthquake hit Taiwan as many people there were preparing to travel for Tomb Sweeping Day, a holiday across the Chinese-speaking world when people mourn the dead and make offerings at their graves. Officials warned the public to stay away from visiting tombs in mountain areas as a precaution, especially because rain was forecast in the coming days.

TSMC, the world’s biggest maker of advanced semiconductors, briefly evacuated workers from its factories but said a few hours later that they were returning to work. Chip production is highly precise, and even short shutdowns can cost millions of dollars.

Christopher Buckley

Lai Ching-te, Taiwan’s vice president, who is also its president-elect, visited the city of Hualien this afternoon to assess the destruction and the rescue efforts, a government announcement said. Mr. Lai, who will become president in May, said the most urgent tasks were rescuing trapped residents and providing medical care. Next, Mr. Lai said, public services must be restored, including transportation, water and power. He said Taiwan Railway’s eastern line could be reopened by Thursday night.

Meaghan Tobin

Taiwan’s fire department has updated its figures, reporting that nine people have died and 934 others have been injured in the quake. Fifty-six people in Hualien County remain trapped.

Shake intensity

Taiwan’s fire department reports that nine people have died and 882 others have been injured in Taiwan. In Hualien County, 131 people remain trapped.

Agnes Chang

Footage shows rocks tumbling down one side of Guishan Island, a popular spot for hiking known as Turtle Island, off the northeast coast of Taiwan. Officials said no fishermen or tourists were injured after the landslide.

The death toll has risen to nine, according to Taiwan government statistics.

Meaghan Tobin, Siyi Zhao

Officials in Taiwan warned residents to not visit their relatives' tombs, especially in the mountains, this weekend during the holiday, known as Ching Ming, meant to honor them. There had already been 100 aftershocks and the forecast called for rain, which could make travel conditions on damaged roads more treacherous.

Crews are working to reach people trapped on blocked roads. As of 1 p.m. local time, roads were impassable due to damage and fallen rock in 19 places, according to the Ministry of Transportation. At least 77 people remain trapped. A bridge before Daqingshui Tunnel appeared to have completely collapsed.

Taiwan’s worst rail disaster in decades — a train derailment in 2021 that killed 49 people — took place on the first day of the Tomb Sweeping holiday period that year, in the same region as the earthquake.

The earthquake hit Taiwan as many people here were preparing to travel for Tomb Sweeping Day, or Ching Ming, a day across the Chinese-speaking world when people mourn their dead, especially by making offerings at their graves. Now those plans will be disrupted for many Taiwanese.

The holiday weekend would typically see a spike in travel as people visit family across Taiwan. Currently, both rail transport and highways are blocked in parts of Hualien, said Transport Minister Wang Guo-cai. Work is underway to restore rail transportation in Hualien, and two-way traffic is expected to be restored at noon on Thursday, he said.

Taiwan’s preparedness has evolved in response to past quakes.

Taiwan’s earthquake preparedness has evolved over the past few decades in response to some of the island’s largest and most destructive quakes .

In the years after a 7.6 magnitude earthquake in central Taiwan killed nearly 2,500 people in 1999, the authorities established an urban search-and-rescue team and opened several emergency medical operation centers, among other measures .

And in 2018, after a quake in the eastern coastal city of Hualien killed 17 people and caused several buildings to partially collapse, the government ordered a wave of building inspections .

Taiwan has also been improving its early warning system for earthquakes since the 1980s. And two years ago, it rolled out new building codes that, among other things, require owners of vulnerable buildings to install ad-hoc structural reinforcements.

So how well prepared was Taiwan when a 7.4 magnitude quake struck near Hualien on Wednesday morning, killing at least seven people and injuring hundreds more?

Across the island, one building collapsed entirely, 15 others were in a state of partial collapse and another 67 were damaged, the island’s fire department said on Wednesday afternoon . Structural engineers could not immediately be reached for comment to assess that damage, or the extent to which building codes and other regulations might have either contributed to it or prevented worse destruction.

As for search-and-rescue preparedness, Taiwan is generally in very good shape, said Steve Glassey, an expert in disaster response who lives in New Zealand.

“ The skill sets, the capabilities, the equipment, the training is second to none,” said Dr. Glassey, who worked with Taipei’s urban search-and-rescue team during the response to a devastating 2011 earthquake in Christchurch, New Zealand. “They’re a very sharp operation.”

But even the best urban search-and-rescue team will be stretched thin if an earthquake causes multiple buildings to collapse, Dr. Glassey said.

Taiwan has options for requesting international help with search-and-rescue efforts. It could directly ask another country, or countries, to send personnel. And if multiple teams were to get involved, it could ask the United Nations to help coordinate them, as it did after the 1999 earthquake.

Pierre Peron, a spokesman for the United Nations, said on Wednesday afternoon that no such request had yet been made as a result of the latest earthquake.

Meaghan Tobin contributed reporting.

At least seven people have died and 736 have been injured as a result of the earthquake, according to Taiwan’s fire department. Another 77 people remained trapped in Hualien County, many of them on hiking trails. Search and rescue operations are underway, said the fire department.

Aftershocks of magnitudes between 6.5 and 7 were likely to occur over the next three or four days, said Wu Chien-fu, director of the Taiwanese Central Weather Administration’s Seismology Center, at a news conference.

As of 2 p.m., 711 people had been injured across Taiwan, the fire department said, and 77 people in Hualien County remained trapped. The four who were known to have died were in Hualien.

Victoria Kim

Hualien County is a quiet and scenic tourist destination.

Hualien County on Taiwan’s east coast is a scenic, sleepy tourist area tucked away from the island’s urban centers, with a famous gorge and aquamarine waters. It also happens to sit on several active faults , making it prone to earthquakes.

The county has a population of about 300,000, according to the 2020 census, about a third of whom live in the coastal city of Hualien, the county seat. It is one of the most sparsely populated parts of Taiwan. About three hours by train from the capital, Taipei, the city describes itself as the first place on the island that’s touched by the sun.

Hualien County is home to Taroko National Park, one of Taiwan’s most popular scenic areas. Visitors come to explore the Taroko Gorge, a striated marble canyon carved by the Liwu River, which cuts through mountains that rise steeply from the coast. The city of Hualien is a popular destination as a gateway to the national park.

According to the state-owned Central News Agency, three hikers were trapped on a trail near the entrance to the gorge on Wednesday, after the quake sent rocks falling. Two of them were found dead, the news agency said. Administrators said many roads within the park had been cut off by the earthquake, potentially trapping hikers, according to the report.

Earthquakes have rattled Hualien with some regularity. In 2018, 17 people were killed and hundreds of others injured when a magnitude 6.5 quake struck just before midnight, its epicenter a short distance northeast of the city of Hualien.

Many of the victims in that quake were in a 12-story building that was severely tilted, the first four floors of which were largely crushed, according to news reports from the time. The next year, the area was shaken by a 6.1-magnitude earthquake that injured 17 people.

The area has some of the highest concentrations of Taiwan’s aboriginal population, with several of the island’s Indigenous tribes calling the county home .

The county government in Hualien released a list of people that had been hospitalized with injuries, which stood at 118 people as of midday Wednesday.

Across Taiwan, one building fell down entirely, in Changhua County on the west coast, and 15 buildings partially collapsed, Taiwan’s fire department said. Another 67 buildings were damaged. One of the partially collapsed structures was a warehouse in New Taipei City where four people were rescued, according to Taiwan’s Central News Agency. Another 12 were rescued at a separate New Taipei City building where the foundation sank into the ground.

Peggy Jiang, who manages The Good Kid, a children’s bookstore down the street from the partially collapsed Uranus Building in Hualien, said it was a good thing they had yet to open when the quake struck. The area is now blocked off by police and rescue vehicles. “Most people in Hualien are used to earthquakes,” she said. “But this one was particularly scary, many people ran in the street immediately afterward.”

Lin Jung, 36, who manages a shop selling sneakers in Hualien, said he had been at home getting ready to take his 16-month-old baby to a medical appointment when the earthquake struck. He said it felt at first like a series of small shocks, then “suddenly it turned to an intense earthquake shaking up and down.” The glass cover of a ceiling lamp fell and shattered. “All I could do was protect my baby.”

Chris Buckley ,  Paul Mozur ,  Meaghan Tobin and John Yoon

The earthquake damaged buildings and a highway in Hualien.

The magnitude 7.4 earthquake that struck Taiwan on Wednesday damaged many buildings and a major highway in Hualien, a city on the eastern coast, and it knocked out power as it rocked the island.

Across Taiwan, the quake and its aftershocks caused one building to completely collapse and 15 others to partially collapse, according to Taiwan’s fire department. Sixty-seven other buildings sustained damage.

Two tall buildings in Hualien that sustained particularly extensive damage were at the center of the rescue efforts there. Most damage across the city was not life-threatening, said Huang Hsuan-wan, a reporter for a local news site.

Where buildings were reported damaged in Hualien City

“A lot of roads were blocked off. There are a lot of walls toppled over onto cars,” Derik du Plessis, 44, a South African resident of Hualien, said shortly after the earthquake. He described people rushing around the city to check on their houses and pick up their children. One of his friends lost her house, he said.

One of the damaged buildings in Hualien, a 10-story structure called the Uranus Building that housed a mix of homes and shops, was tilted over and appeared to be on the verge of collapse. Many of its residents managed to flee, but some were missing, said Sunny Wang, a journalist based in the city. Rescuers were trying to reach the basement, concerned that people might be trapped there.

Photographs of the initial damage in Hualien showed another building, a five-story structure, leaning to one side, with crushed motorcycles visible at the ground-floor level. Bricks had fallen off another high-rise, leaving cracks and holes in the walls.

The quake also set off at least nine landslides on Suhua Highway in Hualien, according to Taiwan’s Central News Agency, which said part of the road had collapsed.

Taiwan’s fire department said four people had been killed in the earthquake.

Across Taiwan, 40 flights have been canceled or delayed because of the earthquake, according to Taiwan’s Central Emergency Operation Center.

President Tsai Ing-wen visited Taiwan’s national emergency response center this morning, where she was briefed about the response efforts underway by members of the ministries of defense, transportation, economic affairs and agriculture, as well as the fire department.

A look at Taiwan’s strongest earthquakes.

The magnitude 7.4 earthquake that hit Taiwan on Wednesday morning was the strongest in 25 years, the island’s Central Weather Administration said.

At least four people died after the quake struck off Taiwan’s east coast, officials said.

Here’s a look back at some of the major earthquakes in modern Taiwanese history:

Taichung, 1935

Taiwan’s deadliest quake registered a magnitude of 7.1 and struck near the island’s west coast in April 1935, killing more than 3,200 people, according to the Central Weather Administration. More than 12,000 others were injured and more than 50,000 homes were destroyed or damaged.

Tainan, 1941

A magnitude 7.3 earthquake in December 1941, which struck southwestern Taiwan, caused several hundred deaths, the United States Geological Survey said.

Chi-Chi, 1999

A 7.6 magnitude earthquake in central Taiwan killed nearly 2,500 people in September 1999. The quake, which struck about 90 miles south-southwest of Taipei, was the second-deadliest in the island’s history, according to the U.S.G.S. and the Central Weather Administration. More than 10,000 people were injured and more than 100,000 homes were destroyed or damaged.

Yujing, 2016

A 6.4 magnitude earthquake in February 2016 caused a 17-story apartment complex in southwestern Taiwan to collapse, killing at least 114 people . The U.S.G.S. later said that 90 earthquakes of that scale or greater had occurred within 250 kilometers, or 155 miles, of that quake’s location over the previous 100 years.

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