In another experiment, a split brain patient is asked to identify an object – such as a pencil – by reaching inside a bag and feeling it. Success depends on which hand does the reaching. Most of the wiring in the body is arranged contralaterally, with the left hemisphere getting its information from – and controlling – the right side of the body, and vice-versa. Since the left hemisphere normally controls language, when the patient reaches in the bag with his right hand he can readily identify the object. However, if the left hand does the reaching, only the right hemisphere gets the information that the object is a pencil, and is powerless to direct the voice to express this. Occasionally, it seems, a patient’s right hemisphere will hit upon a clever stratagem. By finding the point of a pencil and digging it into his palm, he causes a sharp pain to be sent up the left arm. Some pain fibers are ipsilaterally wired, thus the language-controlling hemisphere gets a clue: it is something sharp enough to cause a pain. “It’s sharp – it’s perhaps a pen? A pencil?” The right hemisphere, overhearing this vocalization, may help it along with some hints – discouraging the pen response, encouraging the pencil – so that by a brief bout of Twenty Questions the left hemisphere is led to the correct answer.
Thus, the right hemisphere may occasionally use other forms of communication in order to compensate for the nonexistent corpus callosum.
These experiments, pioneered by Sperry and colleagues, provided insight into the functionings of the two hemispheres and how they are different.
Until recently it has been believed that the entire corpus callosum must be severed to provide proper relief from the severe epilepsy the surgery was trying to negate. However this is not necessarily the case, the corpus callosum might be able to be severed enough to provide relief, without losing all neural integration.
Dr. H. G. Gordon, a neurobiologist at the California Institute of Technology says the connections at the back of the brain alone are enough to integrate both human hemispheres. Speaking for a California research team, he reported a new form of surgery, devised by P. J. Vogel of Los Angeles, which 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. ”
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.
The splenium of the corpus callosum has been found to be the dominant path of the visual aspects of hemispheric integration. Whereas the genus has been found to control motor aspects. For this new procedure, the motor aspects much more pertinent to epilepsy seizures, are severed, while the splenium, the center of visual cross over, remain intact
. This would make the procedure required for severe epilepsy much safer and more practical. The patient would be relieved of the extreme seizures, while retaining interhemisphereic visual pathways and some other communication between hemispheres.
This procedure is now widely used in place of the complete corpus commissurotomy, and experiments are being done with exactly how much of the brain needs commissured. The procedure doesn’t perfectly integrate the two hemispheres, it has been found that callosal transfer times are significantly slower after the operation has occurred. This is thought to be because visual transfer time across the corpus is slower then the motor transfer time. Also bimanual coordination is thought to be somewhat inhibited by this procedure. Never the less, there is definite progress over the complete loss of communication which was thought to happen in the original split brain subjects.
Studying split brain patients’ unusual behaviors has led us to discover valuable information about differences between the two hemispheres. The first of the human split-brain studies began when Michael Gazzaniga joined Roger Sperry as a graduate student at California Tech. In collaboration with neurosurgeon Joseph Bogen, they began a series of commisurotomies. The operation on their first patient, WJ, was a great success. Before the operation he integrated information between the two hemispheres freely, but after the operation he had two separate minds or mental systems, each with its own abilities to learn, remember, and experience emotion and behavior. Yet, WJ, was not completely aware of the changes in his brain. As Gazzaniga put it: “WJ lives happily in Downey, California, with no sense of the enormity of the findings or for that matter any awareness that he had changed.” As previously explained(experiments), words flashed to the right field of vision of patients like WJ could be said and written with the right hand. In contrast, patients couldn’t say or write words flashed to their left field of vision. Although standard experiments revealed that right hemisphere is nonverbal, it is far from incompetent. Even though the right hemisphere could not communicate to observers what stimuli it had been presented with, it did show some verbal comprehension. Even though the patient could not verbalize what word had been presented to the right hemisphere, the left hand was able to point to it within a list.
Another interesting difference between the hemispheres that these patients displayed was that the right hemisphere was distinctly superior in spatial tasks such as arranging blocks and drawing in three dimensions. Researchers showed each hemisphere a simple drawing and had the corresponding hand draw it. Even though all three of the subjects were right-handed, the left-hand drawings were clearly superior.
Because of these hemispheric differences and specializations, split-brain patients have some unusual traits. For example, they are less likely to talk about their feelings, as if they’re unavailable for discussion. The patients give evidence of having two differing minds. The best example of this is patient Paul S. Paul’s right hemisphere developed considerable language ability sometime previous to the operation. Although it is uncommon, occasionally the right hemisphere may share substantial neural circuits with, or even dominate, the left hemisphere’s centers for language comprehension and production. The fact that Paul’s right hemisphere was so well developed in it’s verbal capacity opened a closed door for researchers. For almost all split brain patients, the thoughts and perceptions of the right hemisphere are locked away from expression. Researchers were finally able to interview both hemispheres on their views about friendship, love, hate and aspirations.
Paul’s right hemisphere stated that he wanted to be an automobile racer while his left hemisphere wanted to be a draftsman. Both hemispheres were asked to write whether they liked or disliked a series of items. The study was performed during the Watergate scandal, and one of the items was Richard Nixon. Paul’s right hemisphere expressed “dislike,” while his left expressed “like.” Most split-brain patients would not be able to express the opinions of their right hemispheres as Paul S. did, but this gives us insight on the hidden differences between the hemispheres.
These hidden differences are allowed to demonstrate themselves after a split brain operation because the two hemispheres are closer to existing independently. One hemisphere may not be able to suppress or influence differing opinions, emotions, or desires of the other because most of the communication between the two can no longer occur. As a result, conflicting hemispheric desires or opinions can cause split brain patients to exhibit some strange behaviors. One patient found his left hand struggling against his right hand when trying to pull up his pants in the morning. While the right hand tried to pull them up, the left was trying to pull them down. On another occasion, he was angry with his wife and attacked her with his left hand while simultaneously trying to protect her with his right!
Split-brain patients have also taught us about dreaming. Scientists had hypothesized that dreaming is a right hemisphere activity, but they found that split brain patients do report dreaming. They found, therefore, that the left hemisphere must have some access to dream material. What was most interesting was the actual content of the dreams of the split-brain patients. Klaus Hoppe, a psychoanalyst, analyzed the dreams of twelve patients. He found that the dreams were not like the dreams of most normal people. ” The content of the dreams reflected reality, affect, and drives. Even in the more elaborate dream, there was a remarkable lack of distortion of latent dream thoughts. The findings show that the left hemisphere alone is able to produce dreams. Patients, after commisurotomy, reveal a paucity of dreams, fantasies, and symbols. Their dreams lack the characteristics of dream work; their fantasies are unimaginative, utilitarian, and tied to reality; their symbolization is concretistic, discursive, and rigid.”
These studies of abnormalities of split brain patients as opposed to normal people are providing much insight on hemispheric specialization. Even if some people cannot play the piano correctly, put on a pair of pants, or even comb their hair properly, they can achieve a certain amount of normalcy in their lives by controlling the seizures that affected them previously. They can as well gain some comfort in the knowledge that their ailments are helping psychobiologists learn more about the brain and its functions than ever before.