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Split-brain or callosal syndrome is a type of disconnection syndrome 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 (corpus callosotomy) involves 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. After the right and left brain are separated, each hemisphere will have its own separate perception, concepts, and impulses to act. There was a case in which, when one split-brain patient would dress himself, sometimes he pulled his pants up with one hand (the side of his brain that wanted to get dressed) and down with the other (the side that did not). He was also reported to have grabbed his wife with his left hand and shook her violently, at which point his right hand came to her aid and grabbed the aggressive left hand (a phenomenon sometimes occurring, known as alien hand syndrome). When split-brain patients are shown an image only in the left half of each eye's visual field, they cannot verbally name what they have seen. Communication between the two hemispheres is inhibited, so the patient cannot say out loud the name of that which the right side of the brain is seeing. A similar effect occurs if a split-brain patient touches an object with only the left hand while receiving no visual cues in the right visual field; the patient will be unable to name the object, as each cerebral hemisphere of the primary somatosensory cortex only contains a tactile representation of the opposite side of the body. If the speech-control center is on the right side of the brain, the same effect can be achieved by presenting the image or object to only the right visual field or hand. For example, a patient with split brain is shown a picture of a chicken foot and a snowy field in separate visual fields and asked to choose from a list of words the best association with the pictures.

Additionally, research performed by Roger Sperry and his colleagues later suggested that severing interhemispheric connections to treat severe epilepsy was revealed by functional capacities in the right hemisphere. Their report in the 1967 Scientific American report titled, "The Split Brain in Man," examined how the two hemispheres function independently of one another after a corpus callosotomy. This is a surgical procedure used to treat severe epilepsy by severing the corpus callosum.

Each hemisphere has received the visual information, but only the left hemisphere could verbally report it.

Images were presented to the right hemisphere only.

The right hemisphere controls the primary sensory functions of the left side of the body.

When the experimenter asks the right visual field / left hemisphere what they see the participant will respond verbally, whereas if the experimenter asks the left visual field / right hemisphere what they see the participant will not be able to respond verbally but will pick up the appropriate object with their left hand.

The right hemisphere was found superior to the left hemisphere on modified versions of spatial relations tests and in locations testing, whereas the left hemisphere was more object based.

Sperry found that in humans, the left hemisphere of the brain functions in language processing, but the right hemisphere processes spatial information.

He also had developed language areas in both hemispheres, something very uncommon in split-brain patients. Although Peek did not undergo corpus callosotomy, he is considered a natural split-brain patient and is critical to understanding the importance of the corpus callosum.

Quick Facts

• When split-brain patients are shown an image only in the left half of each eye's visual field, they cannot verbally name what they have seen.
• If the speech-control center is on the right side of the brain, the same effect can be achieved by presenting the image or object to only the right visual field or hand.
• There was a case in which, when one split-brain patient would dress himself, sometimes he pulled his pants up with one hand (the side of his brain that wanted to get dressed) and down with the other (the side that did not).
• The surgical operation to produce this condition (corpus callosotomy) involves transection of the corpus callosum, and is usually a last resort to treat refractory epilepsy.
• Communication between the two hemispheres is inhibited, so the patient cannot say out loud the name of that which the right side of the brain is seeing.

Source material: Wikipedia - "Split-brain". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.