Research: The Left and Right Hemispheres (1)

"Each left and right hemisphere has its own private chain of memories and learning experiences that are inaccessible to recall by the other hemisphere. In many respects, each disconnected hemisphere appears to have a separate mind of its own."  R. W. Sperry

In this section Buzan is drawing attention on information processing in the brain.

Currently there is a tremendous amount of interest in how each cerebral hemisphere process information, how information is shared between the hemispheres, and how the two hemispheres work together to process information.

The pioneering work in this area was conducted by R. W. Sperry and his associates at the California Institute of Technology.

In 1940, two articles appeared in the literature dealing with the corpus coliseum, a huge band of nerve fibers which relay information between the two cerebral hemispheres. T. C. Erickson published an article describing how an epileptic discharge of activity spread from the one hemisphere to the other via the corpus coliseum in the brains of monkeys. Van Wagenen and Herren also published an article describing how damage to the corpus coliseum often reduced the number of seizures experienced by human epileptics.

The above two studies led to a radical treatment for humans with epilepsy who did not respond to traditional treatments. This new treatment, involving severing the corpus coliseum, was termed "split-brain surgery".

Sperry and his associates had done a great deal of experimental work with cats that had the optic chiasm severed. In a normal cat, or human, information from each eye goes to both hemispheres. By severing the optic chiasm, the information from each eye goes only to the ipsi-lateral or same-side hemisphere. That is, information from the left eye goes only to the left hemisphere and information from the right eye goes only to the right hemisphere.

Sperry showed that, when information goes to only one hemisphere in a cat with the corpus coliseum split, the information is not available to the other hemisphere. Sperry was the first to investigate the effects of the split-brain surgery on human epileptics. One experiment that is representative of Sperry’s work is described as follows:

A split-brain patient is seated in front of a screen and is asked to look directly at a black dot in the center of the screen. A picture of a cup is flashed briefly to the right of the dot. This information is lateralised, or delivered only, to her left hemisphere. The subject is asked what she saw. Since the information went to the left hemisphere, or speaking hemisphere, the subject answers ‘cup’. A picture of a fork is then flashed to the left of the dot. This information is lateralised to the right or non-speaking hemisphere. When the subject is asked what she saw, she says ‘nothing’, since the right hemisphere cannot produce language.

However, if she is asked to reach under the screen with her left hand (controlled by the right hemisphere) and pick out the object she saw from a number of hidden objects, she is able to do this. If she is then asked to name the object that she has picked out, she cannot verbalize the response (Sperry, 1968).

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