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Biology 202
2001 Second Web Report
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The Split Brain: Some Thoughts

Nazia Ahmed

"Left, right, left, right--the marching song of the two-mind movement. To hear them talk, you'd think that everyone had a second mind, suppressed by the first. That the vocal left brain dominated the poor artistic right brain. Preventing it from getting a creative thought in edgewise. Soon there will be a consciousness raising movement: Stop referring to the left cerebral hemisphere as the "dominant" one. Invent a more egalitarian term like co-chairperson. Co-chairhemisphere?" William H. Calvin, "Left Brain, Right Brain: Science or the New Phrenology."

The brain is separated into two hemispheres in your brain, the right and the left. At first glance these hemispheres appear to be mirror images of one another, but on closer observations the two hemispheres have highly specialized regions that serve differing functions (1). In general, the right hemisphere interprets information and controls actions of the left side of the body. The left hemisphere interprets information and controls actions of the right side of the body. A thick band of fiber called the corpus callosum connects the two hemispheres. Evidently if the connection between the hemispheres is severed, a once common practice to relieve epileptic attacks, sensory information cannot pass to the correct region of the brain in order for a corresponding response to be made (2). Thus, your brain is SPLIT...!

To me the split brain theory seemed a bizarre notion. Isn't my brain a whole- controlled by the centrally located "little man" who receives my thoughts, processes and multiple functions of my brain? If this is true how could the brain be split into two? Do you have two "yous" then?

The split brain effect was first discovered by Roger Sperry and Ronald Meyers in the early 1960s (3). Meyers and Sperry showed that when the cat had its optic chiasm and corpus callosum severed, two independent learning centers were established - one in each hemisphere of the cat's brain. If the cat had its right eye open and its left eye covered and learned to make a simple conditioned response, it was unable to make the same response when the right eye was covered and the left eye was open. It was as if the learning was unable to be communicated to the other side of the brain (2); thus, it was obvious that information available to one side remained off-limits to the other. Sperry concluded that the brain had, "Two separate realms of conscious awareness; two sensing, perceiving, thinking and remembering systems." (3)

A little disconcerting. At least it had not been proven on humans.

The World War II veteran - known in the scientific literature as W.J.- had undergone surgery to alleviate his epileptic seizures. After the surgery W.J. easily named and described colors, letters, and other information flashed briefly to the right side of his visual field; therefore, W.J.'s left hemisphere needed no help handling basic tasks requiring verbal responses. Then the scientists flashed items in W.J.'s left visual field and waited for the responses of his right hemisphere. As the anxious investigators looked on, W.J. acted as though he had suddenly gone blind. He insisted that he could not see bursts of light, boldface letters, or anything else presented to him. Yet his left hand, under the control of his right hemisphere, pushed down on a telegraph key each time a visual stimulus appeared, just as the scientists had instructed him to do. The scientist, otherwise known as Gazzaniga, and his coworkers had demonstrated that the human brain is a "duplex operation." (4) (6)

The "duplex theory" brings to mind the Dr Jekyll and Mr. Hyde syndrome but raises an important question- when the "two brains" are isolated is the brain being cut into two parts each carrying the same functions or do each have different functions, different yous?

Right, Left enthusiasts take the Gazzaniga results as an obvious indication to hemisphere specialization. Brain-mapping has caused many functions to be localized to either side of the brain. The left hemisphere they say controls language, sequential things and is logical, rationale and linear. The right hemisphere alternatively is better at holistic, artistic, spatial thinking (1) (6). Since the left hemisphere controls the right side of the body, it is thought that right handers are left hemisphere dominant while the left-handers will be right hemisphere dominant. Thus, why not talk about two minds and thus two yous?

Perhaps the most obvious answer is that the brain psychology is not that easy. For someone like myself who is a right-hander and displays stronger right hemisphere features this seems all the more true. Think about it. Under everyday conditions, both halves receive virtually the same outlook on the world. Life proceeds as though nothing is different about perception. Each half share the same knowledge base and reactive inclinations. Thus, your consciousness is controlled by both hemispheres, there is probably huge crossing-over of functions, and simply short of having your corpus callosum severed you might never experience two "yous." And though research on the subject is ever evolving the little man sitting in your brain will happily direct your thoughts and actions to its needed hemisphere.

WWW Sources

1. 1) Specialization in the Two Hemispheres , Details the specific functions localized in each hemisphere

2) Splitting the Human Brain , Brief and concise overview of "split brain."

3) Psychology: Two Brains? , Explains the earlier Sperry and Meyer experiments of split brain.

4) Human Neurobiology , Split-Brain Research Overview of Gazzaniga's split brain experiment.

5) A Split Brain experiment , A great shockwave plugin that lets you experiment with split brain experiments

6) Hemispheric specialization , Interesting article on hemisphere dominance and language.

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