Shufflebrain

Surgeons had cut into the corpus callosum many years earlier, in an attempt to treat epilepsy. In fact, brain surgery developed in the 1880s after Sir Victor Horsley found that cutting into the brains of laboratory animals could terminate seizures. Until the drug dilantin came along in the 1930's, surgery, when it worked at all, was the only effective therapy for epilepsy. In epilepsy, convulsions occur when electrical discharges sweep the surface of the brain. A diseased locus may initiate the discharges, and removal of the zone may reduce or even eliminate seizures. Often, just an incision works, possibly by setting up countercurrents and short-circuiting the discharge. At any rate, splitting the entire corpus callosum seemed too drastic a measure. What would two half-minds be like?

In the 1950s, Ronald Meyers, a student of Roger Sperry's at California Institute of Technology, showed that cats can lead a fairly normal life even after total disconnection of their cerebral hemispheres. Sperry and his associates soon extended their investigations to include the monkey. The ensuing success prompted two California neurosurgeons, Joseph Bogen and P. J. Vogel, to try the split-brain operation on human beings.

Bogen and Vogel's first patient was an epileptic middle-aged World War II veteran. When he awoke from surgery, he couldn't talk. No doubt to the relief of everyone concerned, his speech did return the next day. His seizures could be controlled. And to outward appearances, he and others who have undergone the operation are "just folks," as Michael Gazzaniga, another former student of Sperry's, said during a lecture.

But the split-brain operation has profound effects, although it took careful observation to detect them. Recall that an object in the left visual field signals the right hemisphere, and vice versa. Taking advantage of this, and presenting visual cues in one field at a time, Gazzaniga discovered that most people who had undergone split-brain operations could read, write, and do arithmetic normally, but only with their left cerebral hemispheres. When tested in their right hemispheres, they seemed illiterate, unable to write, and incapable of adding simple sums. Addressing a symposium a few years ago, Gazzaniga described a typical experiment. He held up the word, HEART, in such a way that H and E, presented in the left visual field, signaled the nonreading right hemisphere, while the rest of the word cued the left hemisphere. "What did you see?" , Gazzaniga asked. His subject responded, "I saw ART." The right hemisphere seemed blind to words. But was the right hemisphere really blind? Worse, did it simply lack intelligence? Or even a human mind?

Gazzaniga soon found that the right side of the cerebrum functioned admirably in nonverbal situations. For instance, when shown a picture of a cup, in such a way that it cued the right hemisphere, the person could reach behind a screen, feel among a collection of objects, and find a cup. In fact, the right hemisphere could manifest profound intelligence and sardonic wit. When presented with a picture of a smoldering cigarette, one subject, instead of matching it with a cigarette, brought forth an ashtray.

Not only is the right side capable of humor, but various studies indicate that people tend to use this hemisphere to comprehend geometric form, textures, and music. It's as though, in most of us, the dominant left side does the mundane jobs of reading, writing, and arithmetic, leaving the right hemisphere free to create and appreciate art.

Lateralization, as hemispheric differentiation is called, need not be investigated with the knife.[3] The psychologist Victor Milstein showed me a visual field-testing rig that he and his colleagues use in screening for brain damage. In fact, some of the best evidence of musical tendencies in the right hemisphere came from a test used by Bogen's group prior to actual surgery. Called the amobarbital test, it was perfected by Bogen in collaboration with another member of Sperry's group, Harold Gordon. Amobarbital is an anesthetic. The test involves injecting anesthetic into either the left or the right common carotid artery in the neck, thus anesthetizing one hemisphere at a time. (Actually, blood from a carotid artery on one side will reach the other side of the brain, through a channel called the circle of Willis. But the volume of blood crossing over is small in relation to what flows to the same side.) Gordon compared audio tapes of Bogen's patients singing before and after either the right or left hemisphere had been put to sleep. With the left hemisphere unconscious and the right one awake, most people sang well. But, with some exceptions, the subjects sang flat and off-key when the right hemisphere was unconscious.