Starting in the 1940s, a small group of individuals had a procedure done where their corpus callosum was surgically split. This was done to provide relief from epileptic seizures that would start in one hemisphere and spread to the other. These procedures were very rare, with some only having partial splits. Because of this, only about 10 people have been fully studied.

Brief History of Brain Splitting Procedure

In studies done with cats, both the corpus callosum and optic chiasm were split so that each eye was connected to its respective hemisphere (right eye with right hemisphere and left eye with left hemisphere). 

In each eye and their respective hemisphere, the cats learned a symbol that was associated with a reward and that the inverse was not (different symbols for the left and right). This learning ability showed that each hemisphere ignored what the other learned.

Studies done on Split-Brain Cats

Beginning in the 1960s, techniques used in studies with split-brain cats were used in order to study split-brain humans. This meant selectively presenting stimuli to one of the hemispheres to test their capabilities.

Studies of Split-Brain Humans

A 'split-brain' individual is a person whose corpus callosum has been surgically severed, halting direct neural communication between the right and left hemispheres. This procedure is sometimes performed as an effective treatment for severe epilepsy to control the spread of seizures. Following the surgery, the lack of interhemispheric connection leads to unique behaviors and reveals the specialized capabilities of each hemisphere.

Split-Brain Individual

Several studies done on split brain humans and other animals  show the functions of each brain hemisphere in isolation from one another.

University of Rochester

New York University

- Hemisphere Specialization Using Split Brain Individuals
- Information Processing in the Hemispheres
- Auditory Specializations in the Hemispheres
- Cerebral Lateralization and Handedness
- Evolution of Hemispheric Asymmetry and Specialization

Subjects in Brain Asymmetry and Lateralization of Function

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

Evolution of Hemispheric Asymmetry and Specialization

Cerebral Laterization and Handedness

Anatomical studies of the primary auditory cortex in the right and left hemispheres show how the different hemispheres play different roles in auditory perception.

- Planum Temporale
- Left Hemisphere and Speech
- Right Hemisphere and Music Perception
- Limits of Auditory Specializations

Auditory Specializations in the Brain Hemispheres

In healthy individuals, studies on brain asymmetry focus primarily on hearing and vision. By directing auditory or visual stimuli to a single hemisphere, researchers can infer functional specializations based on the participants' responses.

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