Commissurotomy | in neurosurgery
Though no effect on behavior was observed after commisurotomy was performed on monkeys, it gave peculiar effects on human perception. Different functions of cognition are predominantly located on one of the hemispheres. For example, Brocas area, crucial for forming sentences, is on most people situated in the left hemisphere ventral to the facial motor cortex. The left hemisphere is referred to as the "talking" hemisphere and the right the "silent". A commisurotomy prevents any sensory input to the silent hemisphere from reaching the talking hemisphere. Since the left visual field is processed in the right hemisphere, a person with a commisurotomy is unable to describe objects to the left, because the "talking" hemisphere has not seen anything. It appears as though the person hadn't seen anything at all, and it doesn't bother him either. It can be demonstrated that stimuli to the right hemisphere for example give emotional response, but because of the severed corpus callosum it cannot be verbalized.