The Human Brain

Our brains weigh about three pounds and are divided into two similar looking but functionally different hemisphere, the right hemisphere and the left hemisphere. Both of which are connected by a large bundle of nerves called the corpus collosum. In some people with severe seizure disorders such as epilepsy, it was found that if this bundle of nerves was severed their seizure would either cease or a the very least be better controlled. From this surgical procedure it was discovered that the two hemispheres had different methods of processing information, as well as controlling parts of the body. The left hemisphere controls the right have of the body and the right hemisphere controls the left side.

While we rely on both hemispheres to process different information, we tend to naturally have one hemisphere that is more dominant than the other. While the brain is an organ that can be seen and held the mind is quite another matter. The mind remains unseen and physically immeasurable, yet appears to be the part of us that controls everything. This surgical procedure called "commissurotomy" was pioneered by Roger Sperry and Ronald Myers in the late nineteen fifties. Initially they began experimenting with cats, and later proceeded to study monkeys. In nineteen sixty-one the first human patient was subject to this new procedure.

The surgery worked well as a cure for patients who suffered from severe epilepsy and did not respond to anti-epileptic drugs. It was soon realized that patients who had a commissurotomy had some interesting difficulties. Patients were not able to communicate information from one hemisphere to the other, almost as thought now had two distinct separate brains. Several experiments were done to test perception in the "split-brain" patients.

In one experiment, a word (for example"fork") was flashed so only the right hemisphere could receive the information. The patient would not be able to say what the word was. However, if the subjet was asked to write what he saw his left hand would begin to write the word "fork". If asked what he had written, the patient would have no idea. He would know that he had written something, because he could feel his hand going through the motion. Yet he could not tell the observers what the word was.

Because there was no longer a connection between the two hemisphere...

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...ell us that the split brain patient may only become conscious of something only if the information about it reaches the circuits that control speech in the left hemisphere. It appears that consciousness of the right hemisphere is largely disjoint from that of the left, the right forms a kind of unconscious mind for the left. This brings us to an interesting question, are the right and left hemispheres of a split-brain patient of different consciousness? The answer is no.

While split-brain patients could be manipulated into displaying two independent cognitive styles, the underlying opinions, memories and emotions were the same. This can be explained anatomically. There are deeper structures of the brain that are critical to emotion and physiological regulation that remain connected. Split brains, actually, are not really split into two but instead form a Y. The fact that basic responses (such as the fear-conditioned responses like the heart rate increase to a visual conditioned stimulus) do cross from one hemisphere to the other even when the corpus callosum has been cut, showing that it crosses in lower pathways in the brain, might indicate the evolution of human consciousness.