A split brain is the condition that results when the corpus callosum is surgically severed, usually to control intractable epilepsy. The two cerebral hemispheres can then operate with a high degree of independence.

Classic studies by Sperry and Gazzaniga showed that information presented only to one hemisphere remains inaccessible to the other. A patient may be unable to name an object placed in the left hand or shown in the left visual field, because the right hemisphere that receives the input lacks speech. Yet the same patient can select the object correctly with the left hand, demonstrating that the right hemisphere still perceives and understands. Under special testing conditions the hemispheres can be induced to make conflicting choices.

In everyday life the intact sensory and motor pathways and the remaining subcortical connections allow split-brain patients to function remarkably well. The surgical cases provided decisive evidence for hemispheric specialization and for the role of the corpus callosum in integrating conscious experience.

When the main bridge between the hemispheres is cut, each side can reveal its own capacities and limits.