SPLITTING THE HUMAN BRAIN

Based upon an article originally syndicated in 1970 by World Book Science Service, William J. Cromie, editor

CHICAGO -- Cutting apart the two hemispheres of the human brain is a drastic step, and it is one of the most controversial operations ever performed. Yet it can succeed, when all else fails, in relieving violent, drug-resistant epileptic seizures.

Controversy stems not from the risk to life the procedures involves. It stems from a Jekyll and Hyde aura surrounding the side effects -- the "Split Brain" syndrome. Your brain houses two minds (and maybe more), not one. And they orchestrate into a single personality if -- and only if -- your cerebral hemispheres communicate. Thus, many neurosurgeons have been reluctant to try the split brain operation for fear of severing all vital communications. But now there may be a way to avoid the Jekyll-Hyde effect.

NERVE FIBERS

Dr. H. G. Gordon, a neurobiologist at the California Institute of Technology says connections at the back of the brain alone are enough to integrate both human minds. Speaking for a California research team, he reported a new form of surgery, devised by P. J. Vogel of Los Angeles, stops seizures completely, or at least renders them treatable with drugs. At the same time, he added "Psychological tests of Vogel's patients yield results identical to those of normal subjects. We conclude, the cerebral hemispheres totally integrate if but a small fraction of the corpus callosum remains intact. "

THE TOOL: CEREBRAL RETRACTOR

The corpus callosum is a broad, thick mass of nerve connecting the cerebral hemispheres. In Vogel's new operation (called anterior cerebral commissurotomy) the surgeon opens the skull, lays back the brain's coverings and, with a tool called a cerebral retractor, exposes the corpus callosum between the two hemispheres.

Then he snips through the front three-fourths of the corpus callosum and, while at it, also severs a pipe-cleaner-sized cross connection known as the anterior commissure. But the back of the corpus callosum -- the splenium -- he leaves intact.

WHY NOW?

Why hadn't neurosurgeons done it like this in the first place? Gordon described how people suffered from the full-blown Jekyll/Hyde reactions with tumors or blood clots pressing on only part of the corpus callosum. Surgeons assumed all connections had to work. "We know now, of course," he said, "this assumption was false."

Gordon and his co-workers J. E. Bogen and Roger Sperry believe the tumors and clots cause waves of inhibition to spread to all parts of the corpus callosum. The shocked nerve fibers simply don't carry impulses from one side of the brain to the other.

Actually, split brain dates back to the 1950's and was discovered in the laboratory by Sperry and Ronald Meyers. Cats came first, followed by monkeys. Then, in 1961, humans joined the list.

TWO SEPARATE REALMS

In a lecture some years ago, Sperry called the brain, "Two separate realms of conscious awareness; two sensing, perceiving, thinking and remembering systems." Sperry's work encouraged Vogel and Bogen to try the split brain operation on people.

Ever since 1886, when Sir Victory Horseley ventured into the living brain, the knife has played an important role in the treatment of epilepsy. And neurologist could tell the surgeon that the corpus callosum is involved in seizures. Partial cuts had been made with mixed success. But severing the entire structure! It was unthinkable -- at least until the work with cats and monkeys.

Michael Gazzaniga, who did his graduate work in Sperry's laboratory, carried out the psychological tests on Vogel and Bogen's early patients. The very first, a middle-aged World War II veteran, gave the surgeons a scare. He couldn't talk after the operation. But, happily, his speech returned a month later.

PETER PIPER PICKED....

Over the years, this loss of speech has not been typical at all. As a matter of fact, the second patient coming out of anesthesia complain, "I have a splitting headache!" And when his nurse asked him how well he could talk, he smiled and answered: "Peter Piper picked a peck of pickle peppers!"

To the casual observer, the early split brain patients appeared perfectly normal. They could talk and read and had no problems recognizing the world about them. The seizures gone, they seemed happy, alert and healthy.

Then Gazzaniga made a startling discovery. If the patient held up something like a comb or a coffee cup in his left hand, he couldn't speak its name. Transferred to the right hand -- no trouble at all.

LOUSE IN LEFT FIELD

The same happened with words. If Gazzaniga held up a card with a printed word like LOUSE visible only in the patient's left visual field, he couldn't read it. Yet the left eye was fine. But Gazzaniga knew that the left visual field flashes only to the right side of the brain. And when Gazzaniga put the LOUSE in the right field, guess what happened. The patient immediately recognized it.

BASIC RULES

Was a person's brain a marriage of genius and idiocy? To find out, Gazzaniga had to understand certain basic rules of perception. Right and left worlds of touch and sight flash into opposite cerebral hemispheres.

Gazzaniga also knew sounds would send signals to both hemispheres simultaneously. He could cue his patient by voice. The psychologist realized, too, that many things people learn and think about are nonverbal. Music. Abstract art. Spatial relationships. Geometry.

He constructed a screen with a slot under which a patient could reach and touch objects but not see them. Gazzaniga placed ten objects behind the screen. Then he focused a picture of one off in the patient's left field of view, signaling the right cerebral hemisphere. "Now, please match up the picture you see with one of the objects you can feel on the other side of the screen," the psychologist said.

No difficulty at all!. The patient passed the matching test as well as any normal person. And even when Gazzaniga tried some tricks, the patient made a wise choice. The image of a cigarette, for example: there wasn't one behind the screen. The patient chose an ashtray, instead.

SMART BUT LAZY

The right cerebral hemisphere wasn't an imbecile, after all. It was highly intelligent. And it was still blessed with imagination and a sense of humor. Illiterate, true! And it was mute. But it was as nimble in abstract geometric logic as the dominant left cerebral hemisphere was with words. It had learned early in life to specialize in certain kinds of memory. And it was word- lazy.

Before the corpus callosum had been cut, if the right hemisphere needed a word, all it had to do was put in a call to the left side. Now it was on its own. It would have to learn to hang on to information coming in from the external world. Indeed, it could do that, too. Within six months, the right cerebral hemisphere was sell on its way to literacy. The day would come when a split brain patient might even read two completely different books at the very same time. In a world of words, the operation might have certain advantages.

THE 3 R's DOMAIN

Over the years, Sperry and his many co-worker shave found the dominant left cerebral hemisphere to be involved with the three R's --reading, writing and arithmetic. The right side, while it may be able to handle some words, is the master of form and geometry and music. And when the right hemisphere does learn to write, it favors shoulder and arm muscles over those of the wrist and hand.

SHUT UP!

Each half brain can hold different emotions about a subject. Split brain patients learn very quickly how to keep both sides in communication. Just like Gazzaniga, they talk the words across. When potential conflicts arise about, say, who gets to use the voice box, the dominant hemisphere automatically wins, thus averting crises before they start. How this can happen with a severed corpus callosum is a good question. Possibly, an impulse reaches down into the brain stem, crosses over to the other side and issues a subconscious "shut up!" to the independent but still somewhat meek and mild right cerebral hemisphere.

INSIGHT FOR ALL HUMANKIND

Split brain operations were the lesser of evils, not experiments; they were therapy to relieve, not create abnormality. Vogel's approach held the promise the stroke of the surgeon's knife would not again willfully divorce the two sides of a human being. Yet the early split brain patients have already lent their personal tragedies to the insight of all humankind*

*For his split brain research, Roger Sperry (1913-1994) shared the 1981 Noble Prize in Physiology and Medicine with David Hubel and Torstein Wiesel.

Go here for abstracts of journal articles on agenesis of the corpus callosum.

Go here to see some pictures of the corpus callosum in pickled human brains.

Press here for MORE information on the durability of the human mind in the severely damaged brain. pietsch@indiana.edu