Split-brain

This article is about the human brain condition. For the phenomenon in computing, see Split-brain (computing).

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. 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. 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). However, such conflicts are very rare. If a conflict arises, one hemisphere usually overrides the other.[1]

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. This is because the brain's experiences of the senses is contralateral. 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.[2]

Different sides of the brain specialize in different functions or processes.

The same effect occurs for visual pairs and reasoning. 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. The patient would choose a chicken to associate with the chicken foot 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").[3]

  1. ^ Coon, Dennis; Mitterer, John O. (January 1, 2012). Introduction to Psychology Gateways to Mind and Behavior. Cengage Learning. p. 65. ISBN 9781111833633.
  2. ^ De Haan, E. H.; Corballis, P. M.; Hillyard, S. A.; Marzi, C. A.; Seth, A.; Lamme, V. A.; Volz, L.; Fabri, M.; Schechter, E.; Bayne, T.; Corballis, M.; Pinto, Y. (2020). "Split-Brain: What We Know Now and Why This is Important for Understanding Consciousness". Neuropsychology Review. 30 (2): 224–233. doi:10.1007/s11065-020-09439-3. PMC 7305066. PMID 32399946.
  3. ^ Gazzaniga, Michael S. (July 1, 2000). "Cerebral specialization and interhemispheric communication: Does the corpus callosum enable the human condition?". Brain. 123 (7): 1293–1326. doi:10.1093/brain/123.7.1293. PMID 10869045.