Split-brain

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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. The surgical operation to produce this condition is called corpus callosotomy. It is performed rarely, usually as a last resort in otherwise intractable epilepsy: to mitigate the risk of accidental physical injury by reducing the severity and violence of epileptic seizures.

A patient with a split brain, when shown an image in his or her left visual field (that is, the left half of what both eyes see), will be unable to name what he or she has seen. This is because the speech-control center is in the left side of the brain in most people, and the image from the left visual field is sent only to the right side of the brain. Since communication between the two sides of the brain is inhibited, the patient cannot name what the right side of the brain is seeing. The person can, however, pick up and show recognition of an object (one within the left overall visual field) with their left hand, since that hand is controlled by the right side of the brain.

Some of the earliest split-brain research was carried out by Roger Wolcott Sperry, and continued when he was joined by Michael Gazzaniga. Results from this research have led to important theories on the lateralization of brain function.

Split-brain patients may sometimes confabulate a rational account of their behavior, if the true motivations cannot be reported since they may depend on processing in the linguistically inaccessible right side of the brain.

There are some theories that the different hemispheres may have different "personalities" and contradictory goals.

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