A view of a brain, seen from the top with a cutaway view that exposes the corpus callosum. The corpus callosum is the largest connection between the two cerebral hemispheres (left/right halves of the brain).
We have introduced a new way to organize the brain into two parts—but what was wrong with dividing it into left and right halves? If there is something wrong with that earlier distinction, have we avoided the problems that beset it—or did we fall into the same trap? In this chapter, we review the history and status of the common left-brain, right-brain narrative.
This story apparently began on a day in February 1962, when a forty-eight-year-old man with intractable epilepsy was brought into an operating room at White Memorial Medical Center in Los Angeles. This was the moment that Roger Sperry, a world-renowned neuroscientist, had long awaited.
For years, Sperry and his colleagues at the California Institute of Technology had surgically separated the left and right sides (also called hemispheres because each is, roughly, half a sphere) of the brains of cats and monkeys, and then tested the animals in experiments that measured cognitive function. He and his team had developed a novel way to plumb the mysteries of the living mammalian brain—and their conclusions from this so-called split-brain research had taken the neuroscientific world by storm.
“They perceive, learn and remember much as normal animals do,” Sperry wrote, in a paper that attracted significant attention inside academia but went virtually unnoticed in the larger world. “However, if one studies such a ‘split-brain’ monkey more carefully . . . one finds that each of the divided hemispheres now has its independent mental sphere or cognitive system. . . . In these respects, it is as if the animals had two separate brains.”1
On that winter day in 1962, Sperry was setting the stage for his first test on a human, William Jenkins.
Jenkins was a military veteran who had suffered grand mal seizures (“brain spasms” that produce massive convulsions)—sometimes as many as ten a day—since surviving a bomb explosion near the end of World War II. He had learned of a radical operation, a version of which had been performed by other doctors two decades before at a Rochester, New York, hospital, that had relieved the symptoms of extreme epilepsy. He was eager for the California surgeons to try it on him. Unlike patients who underwent earlier versions of this operation, Jenkins made a deal with his doctors: Whether or not the surgery reduced his suffering, he agreed to work with Sperry, who would administer postoperative behavioral tests similar in principle to those given to the scientist’s experimental animals. Assuming that Jenkins’s higher cognitive functioning survived the surgery, his ability to respond on command and communicate with speech might give Sperry a quantum boost in his research.
“Even if it doesn’t help my seizures,” Jenkins said before meeting the scalpel, “if you learn something, it will be more worthwhile than anything I’ve been able to do for years.”
The surgeons shaved Jenkins’s head, sterilized and peeled back his scalp, opened two holes into his skull, and began the meticulous work of cutting the corpus callosum, the largest structure that connects the left and right hemispheres of the brains of humans; this structure consists of some 250 million nerve fibers, an impressive piece of brain anatomy. The operation went according to plan and Jenkins recovered without incident; his convulsions were indeed gone, and, like Sperry’s monkeys and cats, on casual observation he seemed cognitively normal.
Six weeks after surgery, Sperry began to study his first split-brain human. Jenkins was gratefully cooperative during weekly sessions that continued for months.
A view of a brain, seen from the top with a cutaway view that exposes the corpus callosum. The corpus callosum is the largest connection between the two cerebral hemispheres (left/right halves of the brain).
Sperry and his colleagues devised ingenious tests by which they could assess the cognitive functioning of each half of Jenkins’s brain, together and in isolation. These tests relied on the established facts that the left hemisphere controls movement of the right side of the body (and vice versa), and the left side of each eye sends information to the left hemisphere and the right side of each eye sends information to the right hemisphere.2 The results confirmed what Sperry had theorized from his studies of cats and monkeys: Each side of the human brain has distinct cognitive capabilities. Encouraged, Sperry and his colleagues pushed on, and by 1974, they had tested fifteen more people who had undergone surgical separation of the right and left hemispheres. The findings confirmed their pioneering conclusion: The two sides of the brain indeed do play measurably different roles in cognitive functioning.
By now, the larger world was paying attention. In 1981, Sperry was awarded the Nobel Prize in Physiology or Medicine for his split-brain research.
“The left hemisphere is the one with speech, as had been known, and it is dominant in all activities involving language, arithmetic, and analysis,” the Nobel jury declared when awarding Sperry the prize. “The right hemisphere, although mute and capable only of simple addition (up to about twenty), is superior to the left hemisphere in, among other things, spatial comprehension—in understanding maps, for example, or recognizing faces.”
Simple logic suggested that this dichotomy could explain why some people tend to be analytical and others tend to be intuitive. Some people soon extrapolated from Sperry’s work and gave birth to a new theory of psychology built on the belief that the left side of the brain is the source of rational thought, logic, and linear thinking, whereas the right is the source of emotion, creativity, and imagination—and that in any person, one side or the other is dominant, making that person either more “left-brained” or “right-brained.”
Sperry’s groundbreaking research reached a wide audience at a time when the public had become fascinated with the brain in general. This was the heyday of print journalism, so when the multimillion-circulation Life Magazine began publishing a dramatically illustrated five-part series about the brain on October 1, 1971, ordinary people took notice.
“Miracles and mysteries on a tantalizing scientific frontier,” the Life cover headline read, above a subhead that proclaimed: “With extraordinary photographs.” And indeed, these photos were extraordinary: dozens of color images, many taken through an electron microscope, of vessels, tissue, neurons, and other parts. A remarkable world, existing inside each of us, was revealed. Hollywood had already brought moviegoers there, in the 1966 Academy Award–winning Fantastic Voyage, which spawned a succession of books, comics, and a TV series.
“It is the most highly organized bit of matter in the universe, this three-pound, electrochemical double handful of cells that thrives on change, allows us to move, see and think, to create, to love and be conscious of our actions,” the Life editors wrote.3
Since man first became aware of its existence, he has struggled to comprehend its miracles and miseries, punching crude holes in the bones that protect it and arbitrarily assigning moral and intellectual values to the lumps and bumps on its outer surface. His goals then and now have been the same: To gain a true understanding of how the brain works and use this knowledge not only to treat disease but to improve the very quality of life. Today, thousands of scientists from dozens of disciplines are pursuing these goals in the ultimate assault on man’s last great scientific frontier on earth.
If Sputnik had inaugurated exploration of outer space, these researchers had embarked on a quest into inner space, as some had started to describe the frontier of the brain. But could they ever really succeed? With purplish prose, the Life editors wrought high drama from the field of neuroscience.
“There are difficulties—and dangers,” the Life editors wrote.
Life magazine’s five-part series on the brain in the autumn of 1971 helped build public interest in neuroscience.
After a decade of intense study, many basic questions remain unanswered. In fact, it is possible that the brain may be governed by principles too complex for it to grasp. And even if man does learn to dismantle the loom that spins out his existence, he will find himself with knowledge that could be misused.
The left brain/right brain story offered reassurance that we could be master of our own brains. This was fertile ground in which a new theory of psychology could take root.
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Even before Sperry’s Nobel Prize, the left brain/right brain story had started to spread through popular culture. It gained momentum two years after the Life magazine series, when the New York Times Sunday Magazine published an article, “We Are Left-Brained or Right-Brained.”
“Two very different persons inhabit our heads,” the article began, “residing in the left and right hemispheres of our brains, the twin shells that cover the central brain stem. One of them is verbal, analytic, dominant. The other is artistic.” The article included a photograph of Sperry in his Caltech laboratory and a drawing of a brain divided into its two hemispheres.
The next year, the distinguished psychologist Robert E. Ornstein wrote the first of his many pieces exploring the concept, and his observations were featured in the July 8, 1974, edition of Time magazine. In 1976, the Harvard Business Review published “Planning on the Left Side and Managing on the Right,” which instructed executives on how better to utilize both halves of their vertically divided brains. The widely circulating Psychology Today in 1977 splashed the left brain/right brain story across its pages. Countless other articles were published in specialized and general-interest outlets. A flurry of books began to appear.
Little wonder: The left brain/right brain story appealed both to those with an interest in psychology and to those who wanted only to improve themselves. The claims seemed to be based on solid science. They promised practical advice not only for personal matters but also for relationships and work.
This was not science for science’s sake but a path to a better life that anyone could follow.
Although he did indeed document profound differences between the functioning of the left and right cerebral hemispheres, Sperry did not intend his research to become the basis for a new branch of psychology.4 In a 1984 essay published in the journal Neuropsychologia,5 Sperry warned that “experimentally observed polarity in right-left cognitive style is an idea in general with which it is very easy to run wild . . . it is important to remember that the two hemispheres in the normal intact brain tend regularly to function closely together as a unit.”
And, of course, there was the issue that the patients on whom all of the conclusions were based were just that—patients. They had abnormal brains (otherwise they would never have been operated on). So, there was a lingering question of just how strongly the results from these patients could be assumed to apply to normal people, whose brains are not split into two.
But that was the fine print.
Sperry’s Nobel Prize, announced in October 1981, fueled headline-grabbing publicity. In October alone, the New York Times published ten stories about the scientist and his split-brain work. “On this foundation,” the paper reported, “neuroscientists have postulated further hemispheric divisions of labor; that the left side, for example, may deal with logical, mathematical and analytic thought, while the right side may be the seat of artistic and musical ability.”
Such notions about the left brain and the right brain built on each other and soon became a pop-culture avalanche; outside the research centers, the more nuanced and circumspect findings of neuropsychology and neuroanatomy were mostly lost as the popular version of the left/right theory became widely accepted.
Today, you can watch a YouTube video, as millions already have, of a “Spinning Dancer,”6and you will be asked to answer this question: “Do you see the dancer turning clockwise or anti-clockwise? If clockwise, then you use more of the right side of your brain and vice-versa.” The Spinning Dancer even has its own Wikipedia page (in reality, the “test” is nothing but an optical illusion, and your designation depends on what parts of the figure you pay attention to; it was created by Japanese web designer Nobuyuki Kayahara).
Another self-test promises to reveal whether “your brain is right for a creative career.”7 Still another, which you can take at many sites, purportedly identifies “hemispheric dominance.” Teens can take their own test, the results of which are alleged to be able to “improve your study habits.”8 If the author is to be believed, anyone can benefit from yet another test that assigns precise percentages of “brain usage”9 to each side.
No one, it seems, is too young to benefit. Toys and DVDs can supposedly “develop” your toddler’s left or right side (Stephen Hawking or Georgia O’Keeffe; you choose),10 whereas an older kid might benefit from an ancient calculating device: “How can we motivate BOTH parts of the brain at a time? Learning abacus can accomplish this goal,”11 one merchant asserts. And another Internet site claims that “whole brain integration means using the Left and the Right side of the brain together, which improves the use of your brain by a factor of 5–10%.”12
Those inclined toward effortless improvement can even indulge in “essence therapy,” as it is called: “Left/Right Brain Essence helps restore left/right brain balance,” one ad promises. “Supports physical coordination, meditation, creativity, and mental and emotional balance.”13
The problem is, these claims are wildly exaggerated—to the point where most of them are more popular myth than science.
Researchers have known for decades that none of the sweeping asssertions about left brain/right brain differences are supported by solid science. Although they were not shouting from the mountain-tops, these scientists had unimpeachable evidence that the popular-culture versions of the left brain/right brain theory do not capture how the brain really works.
For example, the left hemisphere is often described as verbal and the right as perceptual—but this distinction doesn’t hold up as a generalization. In reality, both hemispheres typically contribute to both sorts of activities—but do so, often subtly, in different ways.
Consider language: Typically, the left hemisphere produces correct word order—to say, for instance, “I have two left feet” instead of “I two left feet have.” (Yoda’s fractured English may indicate that his alien brain didn’t include a human-standard left hemisphere.) But the right hemisphere also is crucial in language: It extracts the implied meaning—that the speaker doesn’t literally have two left feet but has trouble with physical coordination, much as a person would if she were cursed with actually having two feet shaped like the left one (each with the big toe on the right and the smallest toe on the far left).
And although it is true that the left hemisphere controls speech and plays a major role in grammar and comprehension, the right hemisphere plays a key role not only in our comprehending implied meaning but also in our understanding and producing verbal metaphors and humor, and it is largely responsible for helping us to decipher the meaning of changes in speaking tone, such as the rising tone at the end of a spoken question. And both hemispheres play critical roles in extracting meaning in general. Indeed, neuroimaging studies have conclusively shown that many aspects of language processing are distributed over both hemispheres.14
Similarly, consider perception: For example, if you look at a house, the left hemisphere will allow you to pick up on the shapes of the doors, windows, and other parts, while the right will allow you to take in the overall contours of the building. At the same time, the left hemisphere will specify the relative locations of the parts in terms of categories, such as “the window is left of the front door,” while the right hemisphere will specify locations in terms of specific distances, such as by indicating the precise distance the window is from the door. Again, brain imaging studies have conclusively shown that many aspects of perceptual processing are distributed over both hemispheres.
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The larger issue is not just that people are being classified as “right-brained” or “left-brained” by so-called experts. It’s that the hemispheres are being classified in terms of simple overreaching dichotomies—such as the left’s being verbal, analytic, and logical, and the right’s being perceptual, intuitive, and emotional. It just doesn’t work that way.
Here are the two fundamental problems:
First, it is true that small areas of the brain are specialized in different ways in the two cerebral hemispheres, but these specializations are very specific. For example, a region near the front of the left hemisphere is adept at controlling the movements of the tongue, lips, and vocal cords during speech—but the corresponding part of the right hemisphere plays a crucial role in controlling such movements during singing. Similarly, a region of the left hemisphere under the temples classifies details of visually perceived objects, whereas the corresponding region of the right hemisphere classifies the overall shape of visually perceived objects. In addition, another region under the temples of the left hemisphere organizes speech sounds into the units of a familiar language, whereas the corresponding region in the right hemisphere organizes environmental sounds (such as the sound of rushing water or animal calls). And so on and so forth.
Although small brain areas sometimes do function differently in the two hemispheres, there may not be anything in common that characterizes how they function differently. For instance, what does the difference between controlling speech versus controlling singing have to do with the difference between classifying parts versus classifying overall shapes? So, when you start to group such small areas together into a larger area, any common thread soon breaks—and a simple dichotomy cannot characterize the larger area.
The sorts of documented differences between left-brain and right-brain functioning are hardly the stuff of popular generalizations, but they are fundamentally important to a genuine understanding of brain functioning. The fine print matters.
The second fundamental problem is that each of the specialized brain areas does not work alone but rather works as part of a system that includes many other brain areas—including areas on the opposite side of the brain.
To understand language fully, for example, you need to understand the syntax (the structure of sentences, which is better accomplished by the left hemisphere), the meaning of changes in tone (which is better accomplished by the right hemisphere), and how meaning is deciphered (which is accomplished by both hemispheres working together). In other words, the two hemispheres are part of a single system. Let’s return to our example of a bicycle: It has handlebars, a seat, pedals, gears, a chain, and wheels. All of the parts are designed to work together to accomplish a specific goal (helping a person get from place to place quickly and easily). No one part alone would accomplish much; the power of the machine lies in how the parts all work together. The same is true of the brain.
So the hemispheres do differ, but at a more specific and detailed level than is claimed in the popular press and on the Internet. One half-brain is not “logical” and the other “intuitive,” nor is one more “analytical” and the other more “creative.” Both halves play important roles in logical and intuitive thinking, in analytical and creative thinking, and so forth. All of the popular distinctions involve complex functions, which are accomplished by multiple processes—some of which may operate better in the left hemisphere and some of which may operate better in the right hemisphere—but the overall functions cannot be said to be entirely the province of one or the other hemisphere.
And far from having separate lives, the two halves work together, as Sperry himself noted. They are not isolated systems that compete or engage in some kind of cerebral tug-of-war; one is not an undisciplined child, the other a spoilsport that throws schoolyard tantrums. Rather, as we have stressed, the brain is a single, marvelously complicated, and deeply integrated system. Like those of a well-maintained bicycle, the parts of the brain do have different functions—but, like the parts of a bike, they are designed to work together.
If the pop-culture left-brain/right-brain story is off base, why has it persisted for nearly a half century? Why does a Google search bring millions of hits? Why have such respected figures as Oprah Winfrey15 and best-selling author Daniel Pink16 embraced it?
The answer is not only the intense media attention that Sperry’s work and his Nobel Prize attracted or the power of the Internet today. The answer may lie in our instinctive search for understanding, a timeless narrative of the human experience. As a species, we seem to be hardwired to try to make sense of what we encounter, even something as complex as the brain—and so we create narratives, simplifying them when necessary. This is not inherently a bad thing, provided that the narratives are simplified in the right way—characterizing core ideas and not introducing misconceptions.
It is a testament to the power of the left/right story, and to our tendency to embrace simplified narratives, that this story has persisted despite periodic warnings from scientists and academicians.
As early as 1971, Brenda Milner, a distinguished scientist at the Montreal Neurological Institute, cautioned against overly expansive interpretations of split-brain research in an article published in the British Medical Bulletin.17 In the conclusion to her study, Milner wrote that “although this paper has been written to emphasize the hemispheric differences, one must beware of pushing the contrast too far.” Five years later, Stevan Harnad, founder (in 1978) of the respected journal Behavioral and Brain Sciences, wrote that a black-and-white lateralization dichotomy had “about as much relation to the known facts about hemisphere functioning as astrology does to astronomy.”18
And in 1987, Pace University psychology professor Terence Hines maintained, in Academy of Management Review, that attempts to utilize the left brain/right brain story to improve business performance were like “the pursuit of wild geese,” a pursuit “based on incorrect views of the nature of hemispheric differences, views that can be best termed myths”—his emphasis. The scientific literature holds many more such cautions.
But these contrarian voices were largely unheard—or unheeded—outside academia. Even for some inside the scientific world, the left/right theory proved tantalizing, as psychologist Ornstein remembered in his 1997 book The Right Mind: Making Sense of the Hemispheres. Recalling the experiments of Sperry and others in the 1960s and 1970s, he wrote:
How these demonstrations of split mindedness got all our attention! It caused many people to overestimate the split of the mind and underestimate its unity, even though different sectors of the mind handle the world differently. In real life, one disconnected hemisphere isn’t operating alone or running the whole show. The two are intimately and thoroughly connected, and not only by the corpus callosum, but by all the lower brain structures. And more.
We have argued that a person’s habitual way of thinking does arise from the workings of two portions of the brain, the top and the bottom. And we have argued that simple dichotomies cannot adequately explain what these two portions do: They must be viewed as systems—and systems that work together. In many ways, the interactions between the top-brain and bottom-brain systems are more interesting and informative than the processing that occurs in each system alone. We turn to such interactions in the following chapter.
