As discussed in the experiments on split brain patients, if a perception does not go to the left hemisphere (our center for speech) the patient says they are not conscious of it. (see a standard experiment for a review) However, his right hemisphere is aware of it and can respond accurately. For example, if the person in the experiment was asked to use the object, he would be able to accurately use the key, or if asked to write down the name of the object, the left hand would be able to write the names of simple objects. Even so, the person says they do not know what the left hand is doing. This seems to tell us that we may become conscious of something only if the information about it reach the circuits that control speech in the left hemisphere. It seems that the consciousness of the right hemisphere is largely disjoint from that of the left, the right forms a kind of unconscious mind for the left. It can be disputed that the right hemisphere is not as conscious as the left because it manifests its consciousness in other ways. The right hemisphere has an unconscious knowledge of the stimuli that is presented to it. For example:
"Gazzaniga described an example of flashing a picture of a nude woman amidst a series of ordinary pictures to the left or right hemisphere of a female patient. When the picture was shown to the left hemisphere, the patient laughed and identified the picture. When it was shown to her right hemisphere she said she saw nothing but she laughed. When asked why she laughed, she said she did not know-"Oh, that funny machine."
It is important to note that in these patients the hemispheres are not completely disconnected, the right hemisphere can inject ideas into the left through the brainstem. Split brain patients experience these communications as unexplainable hunches from the unconscious.
This brings us to an interesting question, are the right and left hemispheres of a split brain patient of different consciousness? Sperry rejected this notion, and most scientists agreed with him. While split-brain patients could be manipulated into displaying two independent cognitive styles, the underlying opinions, memories, and emotions were the same. This could be explained anatomically. As discussed earlier, deeper structures of the brain that are critical to emotion and physiological regulation remained 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 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. We might have had these pathways before we developed the consciousness that we have now. This is not surprising, and illustrates how many scientists view the consciousness of other animals, less evolved than ours.
Split brain research has brought scientists closer to
understanding consciousness. And almost as important it is an extremely
interesting topics for undergraduate psychology and biology majors.
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