Everyone knows the popular myths about the two brain hemispheres: The right brain is artistic, musical, spatial, intuitive, and holistic; the left brain is linear, rational, analytical, and linguistic. There is some truth in these labels. But, not surprisingly, they are mostly oversimplifications of tendencies, not fixed rules.

A May 1998 issue of Science reported that a study of an epileptic patient who had undergone a commissurotomy, a procedure that severs all connections between the hemispheres, has shown that speech and writing, two skills believed to exist in the same side of the brain since the time of Paul Broca, “can reside in different hemispheres,” suggesting that written and spoken language can develop independent of one another. This would have been appalling news in 1975; today, it is received without surprise-at least by those who make the study of the brain their business.

“all brains are not organized the same way. Like with everything else human, genes collide with environment and the result is not a predictable thing.”

When I asked split-brain expert and the author of The Lopsided Ape, Michael Corballis, to address some of the conceptions about hemispheric differences, his assessments were very much along these lines.

On the subject of creativity and language-two skills often polarized as examples of right and left brain thinking-Corballis said, “I don’t see any good evidence that the right hemisphere is more creative than the left. Language itself is highly creative-every sentence you construct is a new creation-and one could make a case for supposing that the left hemisphere is really the creative one.” He goes on, “But I think artistic creativity is likely to invoke more right-hemisphere capacities, simply because of the right- hemisphere bias for spatial skills. And there are aspects of language, such as prosody, and perhaps pragmatic aspects such as an understanding of metaphor or sarcasm, that may be more right than left hemispheric. So it’s always a question of balance.”

“Quite simply,” writes Michael Gazzaniga, a former student of split-brain pioneer Roger Sperry, “all brains are not organized the same way.” Like with everything else human, genes collide with environment and the result is not a predictable thing.

In short, our reduction of the sides of the brain to the seats of this or that skill or quality misses the point entirely. “On the whole,” said Corballis, “I think it would be better for educationalists and therapists to forget about the hemispheres and concentrate on the skills themselves. The hemispheres are convenient pegs on which to hang our prejudices.”

The Left Brain Interpreter
Michael Gazzaniga’s recent work in brain lateralization has produced one of the more interesting ideas to come along in the field for a while. The concept is that the left brain possesses a device he calls “the interpreter,” which is always busy trying to make sense of the world. It is this interpreter, argues Gazzaniga, that is responsible for false memories-the lies we make up from time to time to explain our behavior or to fill in forgotten details. As a rule, these lies make logical sense, but, of course, they just aren’t true. So why do we create them?

“It is a common fallacy in neuroscience to suppose that there’s some kind of mind inside the mind to explain how the mind interprets things.”

Studies done with patients who have disconnected hemispheres have revealed that there might be something to the interpreter. Since the right brain is linked to the left half of the body-including the left ear, hand and eye-and the left brain to the right half of the body, researchers are able to communicate directly with one half of the brain or the other in split-brain patients. In Gazzaniga’s study, a patient’s right brain was presented, through the left visual field, with commands like “Walk” or “Laugh.” When the left brain-completely oblivious to the order given the right-was asked why the patient had walked out of the room, it immediately fabricated a reply: “To get a Coke.” When asked why he was laughing, the left brain offered the reply, “You guys come up and test us every month. What a way to make a living!”

When I asked Corballis about the interpreter, he was skeptical. “The trouble with the interpreter,” he said, “is that it’s difficult to distinguish it from the fact that it’s the left hemisphere that has language. If the interpretation is expressed in language (as it almost always is), then it comes from the left hemisphere. The right hemisphere may have its interpretation too, but we may not be able to find out what it is.”

He continued, addressing issues of popular writing about brain research: “Another problem with the interpreter is that it is a sort of personification-a ‘little man’ who sits inside the left brain and interprets things. It is a common fallacy in neuroscience to suppose that there’s some kind of mind inside the mind to explain how the mind interprets things, but this of course leads to an infinite regress. Daniel Dennett, in his book Consciousness Explained, attacks this kind of theorizing, which he calls the “Cartesian Theater” approach, where the mind somehow sets up a stage and the ‘little man,’ or soul, or whatever you want to call it, looks on.”

“That said,” Corballis concedes, “the interpreter does capture some of the evidence in an easy-to-understand way. It’s not really science, but it gets an idea across.”

Looking Back: A History of Hemispheres
Mounting debates about the hemispheres raged among doctors and scientists as early as the nineteenth century, and even occasionally found their way into popular culture. The protagonist of Robert Louis Stevenson’s play “Deacon Brodie: or the Double Life” was a respected cabinet maker by day, and a burglar by night, and Stevenson’s famous story, The Strange Case of Dr. Jekyl and Mr. Hyde (1886) explored further the idea of a cultured left hemisphere in opposition to the primitive and generally out-of-control emotional right hemisphere.

A century later, in 1963, the surgeons Phillip Vogel and Joseph Bogen developed a surgery, called a commissurotomy, in which they severed the immense network of nerve fibers connecting the left and right hemispheres in hopes of stopping the spread of epileptic seizures from one side to the other. As a result, each half of the brain could be studied in isolation from the other. It appeared, indeed, that after the surgery, each hemisphere was completely unaware of the other’s existence-a fact that would prove fortuitous for the study of brain functions.

“[Sperry] found that the split-brain patients displayed a clear ability to function without the benefit of communication between the hemispheres. Included among the early findings was proof that the right brain was sometimes capable of language skills-certainly weaker at the task than the left brain, but capable nonetheless.”

The work of Vogel and Bogen cleared the way for California Institute of Technology physiologist Roger Sperry to run his now-famous tests on the new split-brain patients. When Sperry began testing, he found that the split-brain patients displayed a clear ability to function without the benefit of communication between the hemispheres. Included among the early findings was proof that the right brain was sometimes capable of language skills-certainly weaker at the task than the left brain, but capable nonetheless.

These events heralded in what some have termed dichotomania-the fervent movement that erupted in the 1970s in an attempt to push our society out of our “left brain” thinking, and into a more intuitive, artistic “right brain” mode. Over the next three and a half decades, over 45,000 articles and books-most of them medical and scientific-would be written on the left brain/right brain issue.

As Robert Ornstein, author of The Right Mind, points out, right brain ideology crept into every corner of culture and society during this time, including “Beethoven, biography, photography, drawing, cooking, auto repair, and housekeeping.”

Looking Forward: The Future of Split-Brain Research
The advent of new technologies like fMRI and PET scans have offered some new insights into the respective functions of our brain hemispheres. Because of this technology, there have been a growing number of patients discovered to have been born split-brained, which has provided an entirely new window on brain lateralization, and one without the psychological disconnection resulting from surgery.

Much is also now coming from Dartmouth College, where Michael Gazzaniga heads the Program in Cognitive Neuroscience. The focus of research is beginning to shift to a better understanding of normal brain function, which is probably very different than split-brain function. Interestingly, some recent studies at Dartmouth give credence to the idea-suggested by Corballis in The Lopsided Ape and an earlier work, Human Laterality-that the development of language, in Gazzaniga’s words, “chased the perceptual skill out of the left brain” in the course of evolution.

“There is even more recent evidence,” Corballis explained, when I asked him about this, “that the right hemisphere has these specializations [perceptual and spatial skills] in other species, such as mice, and even chickens, that do not have language, which rather goes against the theory. One might therefore reverse the argument and say that language occupied the left hemisphere precisely because it was less involved in other things. All of this is largely evolutionary speculation; there’s little direct evidence.”

And so, as they say, back to the drawing board. But the drawing board of brain hemispheric research must be among the most interesting around.

References
Gazzaniga, Michael S., “The Split Brain Revisited,” Scientific American, July 1998, p. 35.

Ornstein, Robert, The Right Mind: Making Sense of the Hemispheres. Harcourt Brace and Company, New York: 1997.

Strauss, Evelyn, “Writing, Speech Separated in Split Brain.” Science, May 8, 1998; 280: 827.