Commissurotomy

Split-brain is a lay term to describe the result when the corpus callosum connecting the two halves of the brain is severed to some degree. The surgical operation to produce this condition is called corpus callosotomy. It is rarely performed, usually in the case of 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 (the left half of what each eye sees), 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 the two sides of the brain cannot communicate, the patient can't name what he or she is seeing. The person can, however, pick up a corresponding object with their left hand, since that hand is controlled by the right side of their 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. However, in analyzing this research, it is necessary to remember that the patients involved in these operations had abnormal brains to begin with.