The corpus callosum is the thick band of nerve fibers that links the left and right hemispheres of the brain. It is the largest white-matter structure in the human brain and the main highway for interhemispheric communication.

Sensory, motor, and cognitive information crosses through this bridge so that the two sides of the brain can coordinate. In split-brain patients, whose corpus callosum has been surgically severed to control severe epilepsy, the hemispheres operate with striking independence. A patient may be unable to name an object presented only to the right visual field, or may perform conflicting actions with the two hands. These cases revealed how specialized the hemispheres can become while still remaining part of a single person under normal conditions.

Development of the corpus callosum continues into adolescence. Its size and integrity have been studied in relation to handedness, language lateralization, and certain developmental conditions. Damage from stroke, trauma, or demyelinating disease can disrupt the smooth transfer of information and produce disconnection syndromes.

Every time the two sides of the brain act as one coordinated system, the corpus callosum is carrying the traffic.