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Split-brain is a lay term to describe the result when the corpus callosum connecting the two hemispheres of the brain is severed to some degree. It is an association of symptoms produced by disruption of or interference with the connection between the hemispheres of the brain. The surgical operation to produce this condition results from transection of the corpus callosum, and is usually a last resort to treat refractory epilepsy. Initially, partial callosotomies are performed; if this operation does not succeed, a complete callosotomy is performed to mitigate the risk of accidental physical injury by reducing the severity and violence of epileptic seizures. Before using callosotomies, epilepsy is instead treated through pharmaceutical means. After surgery, neuropsychological assessments are often performed. After the right and left brain are separated, each hemisphere will have its own separate perception, concepts, and impulses to act. Having two "brains" in one body can create some interesting dilemmas. When one split-brain patient dressed himself, he sometimes pulled his pants up with one hand (that side of his brain wanted to get dressed) and down with the other (this side didn't). Also, once he grabbed his wife with his left hand and shook her violently. So his right hand came to her aid and grabbed the aggressive left hand. However, such conflicts are actually rare. If a conflict arises, one hemisphere usually overrides the other. When split-brain patients are shown an image only in their left visual field (the left half of what both eyes take in (see optic tract)), they cannot vocally name what they have seen. This can be explained in three steps: (1) The image seen in the left visual field is sent only to the right side of the brain; (2) For most people, the speech-control center is on the left side of the brain; and (3) Communication between the two sides of the brain is inhibited. Thus, the patient cannot say out loud the name of that which the right side of the brain is seeing. In the case that the speech-control center is on the right side of the brain, the image must now be presented to only the right visual field to achieve the same effect. If a split-brain patient is touching a mysterious object with only the left hand, while also receiving no visual cues in the right visual field, the patient cannot say out loud the name of that which the right side of the brain is touching. This can be explained in three steps: (1) Each cerebral hemisphere of the primary somatosensory cortex only contains a tactile representation of the opposite (contralateral) side of the body; (2) For most humans, the speech-control center is on the left side of the brain; and (3) Communication between the two sides of the brain is inhibited. In the case that the speech-control center is on the right side of the brain, the object must now be touched only with the right hand to achieve the same effect. The same effect occurs for visual pairs and reasoning. For example, a patient with split brain is shown a picture of a chicken and a snowy field in separate visual fields and asked to choose from a list of words the best association with the pictures. The patient would choose a chicken foot to associate with the chicken and a shovel to associate with the snow; however, when asked to reason why the patient chose the shovel, the response would relate to the chicken (e.g. "the shovel is for cleaning out the chicken coop"). "Scientists have often wondered whether split-brain patients, who have had the two hemispheres of their brain surgically disconnected, are 'of two minds'" (Zilmer, 2001). == History == In the 19th century, research on people with certain brain injuries made it possible to suspect that the "language center" in the brain was commonly situated in the left hemisphere. One had observed that people with lesions in two specific areas on the left hemisphere lost their ability to talk, for example. Research was pioneered by Roger Sperry and his colleagues. In his early work on animal subjects, Sperry made many noteworthy discoveries. The results of these studies over the next thirty years later led to Roger Sperry being awarded the Nobel Prize in Physiology or Medicine in 1981. Sperry received the prize for his discoveries concerning the functional specialization of the cerebral hemispheres. With the help of so-called "split brain" patients, he carried out experiments, and for the first time in history, knowledge about the left and right hemispheres was revealed.〔(【引用サイトリンク】url=http://www.nobelprize.org/educational/medicine/split-brain/background.html )〕 In the 1960s Sperry was later joined by Michael Gazzaniga a psychobiology Ph.D. student in his work on split-brain research at Caltech in Pasadena, California. Even though Sperry is considered the founder of split-brain research, Gazzaniga’s clear summaries of their collaborative work are consistently cited in psychology texts. In Sperry and Gazzaniga's, “The Split Brain in Man” experiment published the Scientific American in 1967 they wanted to explore the extent to which two halves of the human brain were able to function independently and whether or not they had separate and unique abilities. They wanted to examine how someone with a split-brain perceptual and intellectual skills were affected. At Caltech, Gazzaniga worked with Sperry on the effects of split-brain surgery on perception, vision and other brain functions. The surgery, which was a treatment for severe epilepsy, involved severing the corpus callosum, which carries signals between the left-brain hemisphere, the seat of speech and analytical capacity, and the right-brain hemisphere, which helps recognize visual patterns. At the point of which this article was written, only ten patients had undergone the surgery to sever their corpus callosum. Four of these patients had consented to participate in Sperry and Gazzaniga’s research. After the corpus callosum severing all four participants personality, intelligence, and emotions appeared to be unaffected. The testing done by Sperry and Gazzaniga showed however, the subjects demonstrated unusual mental abilities. The researchers created three types of tests to analyze the range of cognitive capabilities of the split-brain subjects. The first was to test their visual stimulation abilities, the second test was a tactile stimulation situation and the third tested auditory abilities. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Split-brain」の詳細全文を読む スポンサード リンク
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