Callosum

The corpus callosum, often referred to simply as the callosum, is the largest white‑matter structure in the human brain. It consists of about 200 million axons that connect the left and right cerebral hemispheres, enabling communication between homologous cortical regions. The corpus callosum arches inferior to the cingulate gyrus and forms the roof of the lateral ventricles, subdividing into four regions: the rostrum, the genu, the body, and the splenium.

Functionally, the corpus callosum integrates motor, sensory, and higher‑order cognitive information across hemispheres, coordinates bilateral movements, and contributes to processes such as language, perception, and attention. It contains commissural fibers linking frontal, parietal, temporal, and occipital areas, supporting coordinated, unified brain activity.

Development and variation occur throughout life. The corpus callosum begins forming early in gestation and continues to develop postnatally with progressive myelination into adolescence. Agenesis of the corpus callosum (ACC) is a congenital disorder characterized by partial or complete absence of the structure and may be associated with other brain malformations and neurodevelopmental symptoms. Hypoplasia or dysgenesis can also occur and may accompany various syndromes.

Clinical significance and imaging are important for assessment. In epilepsy, surgical disconnection of the corpus callosum (callosotomy) can reduce seizure spread but may cause disconnection syndromes. Neuroimaging, especially magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI), is used to assess anatomy, detect ACC, lesions, or agenesis, and to map white matter tracts.

Evolutionarily, the corpus callosum is a characteristic feature of placental mammals and varies in size and shape across species. Its integrity is generally associated with the degree of hemispheric specialization and coordination.