The cortex is split into left and right hemispheres, each with its own lobes, which normally communicate through the corpus callosum.
Split-brain patients, whose corpus callosum was cut to stop seizures spreading, revealed that the two hemispheres can specialize in different functions.
The right visual field goes to the left hemisphere and vice versa, and in most people the major language areas are in the left hemisphere.
A split-brain patient can't name an object flashed to the left visual field but can pick it out with the left hand, because of contralateral organization.
Broca's area (left frontal lobe) produces speech, Wernicke's area (left temporal lobe) supports understanding language, and damage to either can cause aphasia.
Key terms
hemispheres
The left and right halves of the cerebral cortex, each with frontal, parietal, temporal, and occipital lobes.
corpus callosum
Thick band of nerve fibers through which the two hemispheres communicate.
split-brain patients
People whose corpus callosum was surgically cut, usually to keep severe epileptic seizures from spreading between hemispheres.
visual field
Everything you see to one side when looking straight ahead; each field is processed by the opposite hemisphere.
contralateral organization
Each hemisphere primarily controls the opposite side of the body.
Broca's area
Area in the left frontal lobe important for producing speech (damage causes broken speech).
Wernicke's area
Area in the left temporal lobe important for understanding language (damage causes word salad).
aphasia
An impairment in producing or understanding language.
Watch out
Broca's = broken speech (trouble producing); Wernicke's = word salad (fluent speech that doesn't make sense).
Left visual field goes to the right hemisphere, which can't say the word but can guide the left hand to the object.