The Human Brain Essay, Research Paper

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 hemispheres, information presented to the right half of the brain can not convey this information to the left half. Interestingly enough, the centers for speech interpretation and production are located in the left hemisphere. If the patient is blindfolded and a familiar object, such as a toothbrush, is placed in his left hand he appears to know what it is; for example by make the gesture of brushing his teeth. If asked by the experimenter to name the object he can not. When asked what he is doing with the object, gesturing a brushing motion, he has know idea. If the left hand gives the toothbrush to the right hand, the patient will immediately say “toothbrush.” Cutting apart the two hemispheres of the human brain is a drastic step, and is one of the most controversial operations ever performed. Controversy stems not from the risk to life the procedure involves. It stems from a Jekyll and Hyde aura surrounding the side effects-the”Split-Brain” syndrome. They orchestrate into a single personality if-and only if-the cerebral hemispheres communicate. Thus, many neurosurgeons have been reluctant to try the split-brain operation for fear of severing all vital communications. However, there may now be a way to avoid the Jekyll-Hyde effect. A new form of the surgery devised by P.J. Vogel called anterior cerebral commissurotomy eliminates the Jekyll-Hyde effect. The procedure involves; opening the skull, laying back the brains coverings, then using a tool called a cerebral retractor to expose the corpus callosum. The front three-fourths of the corpus callosum are then severed, as well as a small cross section of the anterior commissure. This leaves the back of the corpus callosum (called the splenium) intact. Psychological tests of the patients who under went the new procedure yielded results identical to those of normal subjects. However, some unusual behavior was noted in these patients in that, now they appeared to have not only two brains but two distinct mental systems as well. Each with its own abilities to learn, remember and experience emotion and behavior. Another interesting difference between the hemispheres was noted. Patients displayed that the right hemisphere was distinctly superior in spatial tasks such as arranging blocks and drawing three dimensional pictures. Researchers showed identical images to each hemisphere and had the corresponding hand draw the image. Although several of the subjects were right-handed, the left-hand drawings were clearly more superior. Because of these hemispheric differences and specialization’s, split-brain patients have some unusual traits. For example, they are less likely to express their feelings, as if they are unavailable for discussion. The subjects show evidence of two differing minds. Although it is uncommon, the right hemisphere may sometimes share substantial neural circuits with, or even dominate, the left hemisphere’s centers for language comprehension and production. For almost all split-brain patients, the thoughts and perceptions of the right hemisphere are locked away from expression. These hidden differences are allowed to demonstrate themselves after a commissurotomy because the two hemispheres are closer to existing independently. One hemisphere may not be capable of suppressing or influencing differing opinions, emotions, or des ires 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. For example; 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. What is consciousness and what is its usefulness? Consciousness, as defined in psychology: brain, mind and behavior, is the subjective awareness of mental events. It seems that we are aware of many things and these things (thoughts, motives, perceptions and feelings) could be available to consciousness depending on the attention they are given. Attention is the focusing of consciousness by providing heightened sensitivity to a certain stimuli in awareness. For example, while watching television a person might be aware of voices in the next room, the telephone ringing and the smell of breakfast cooking. At a critical point the smell of food burning is unconsciously given perceptual meaning and attention shifts bringing the food into the center of awareness, or consciousness. One of the roles of consciousness therefore seems to be to monitor the self and the environment, and control our thoughts and behavior. However, with split-brain subjects if a perception does not reach the left hemisphere the subject states they are not conscious of it. Although, their right hemisphere is aware of it and can respond accurately. This seems to tell 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.