Corpus callosum

At a glance

English

Corpus callosum

Latin (TA2)

Corpus callosum

System

Brain and spinal cord

Region

Head

Side

Single, on the midline

About the corpus callosum

The corpus callosum is the largest commissure of the brain, a thick flat band of nerve fibres crossing between the two cerebral hemispheres at the bottom of the longitudinal fissure. Its name means tough body. Seen in a midline section it is about ten centimetres long and shaped like a curved hook. Its upper surface is covered by a thin layer of grey matter and is separated from the cingulate gyrus by the callosal sulcus; its lower surface forms much of the roof of both lateral ventricles, with the septum pellucidum and fornix hanging beneath it.

It is described in parts from front to back. The rostrum is a thin beak that runs back and down under the front end, joining the lamina terminalis. It turns upward into the genu, the bend that sits ahead of the septum pellucidum. The trunk, or body, forms the long middle arch. A slight narrowing, the isthmus, comes just before the splenium, the thick rounded back end that overhangs the pineal region and the roof of the third ventricle.

From each part fibres fan out into the hemispheres. Fibres bending forward out of the genu to reach both frontal lobes form the forceps minor; those arching backward out of the splenium to reach both occipital lobes form the forceps major. Fibres of the trunk and splenium sweeping down into the temporal lobes make up the tapetum, which lines the roof and side of the posterior and temporal horns. In broad terms the front links prefrontal areas through thin, lightly myelinated fibres, the trunk joins motor and sensory regions with thicker fast fibres, and the splenium connects parietal and visual cortex. The tract first crosses the midline early in fetal life and keeps maturing into early adulthood.

Cutting the corpus callosum (callosotomy) is used to stop seizures spreading from one hemisphere to the other in severe epilepsy, and it reveals the split-brain picture in which each hemisphere works with little knowledge of the other. The callosum may fail to form, wholly or partly, sometimes with no symptoms. It is a typical site of multiple sclerosis plaques, and damage to the splenium can cause alexia without agraphia.

Function and supply

Function

Carries information between matching regions of the two cerebral hemispheres so that perception, movement and thought on both sides are coordinated.

Blood supply

Pericallosal branches of the anterior cerebral artery supply roughly the front four fifths; the splenium receives splenial branches of the posterior cerebral artery.