The corpus callosum is a structure located within the brain and connecting the two left and right hemispheres.

Position. The corpus callosum is the main junction between the left and right hemispheres of the brain (1). It is located at the center and towards the bottom of the two hemispheres. The upper surface of the corpus callosum is thus in contact with the hemispheres.

Structure. Arch-shaped, the corpus callosum is a bundle made up of an average of 200 million nerve fibers. These fibers grow through the white matter of different lobes or areas of the hemispheres.

The corpus callosum is made up of four distinct areas, which are, from front to back (1):

• The rostrum, or beak, connecting the left and right frontal lobes;
• The knee, connecting the left and right parietal lobes;
• The trunk, connecting the left and right temporal lobes;
• And selenium, connecting the left and right occipital lobes.

Vascularization. The corpus callosum is supplied by the two anterior cerebral arteries, with the exception of the splenium. The latter is partly vascularized by the branches of the posterior cerebral artery (1).

Communication between the two hemispheres. The corpus callosum plays a central role in the transfer of information between the left and right hemispheres of the brain. This communication thus allows the coordination of the two hemispheres, the interpretation of information and the action accordingly (1).

An integral part of the central nervous system, the corpus callosum can be the site of numerous pathologies, the causes of which may be of inflammatory, infectious, tumor, vascular, traumatic origin or may be linked to abnormalities.

Agenesis of the corpus callosum. The corpus callosum can be the site of malformations, one of the most frequent of which is agenesis.

Head trauma. It corresponds to a shock to the skull which can cause brain damage. (2) These lesions can be concussions, i.e. reversible lesions, or contusions, irreversible lesions (3).

Stroke. Cerebrovascular accident, or stroke, is manifested by obstruction, such as the formation of blood clots or the rupture of a blood vessel in the brain. (4) This pathology can impact on the functions of the corpus callosum.

Brain tumors. Benign or malignant tumors can develop in the corpus callosum. (5)

Multiple sclerosis. This pathology is an autoimmune disease of the central nervous system. The immune system attacks the myelin, the sheath surrounding nerve fibers, causing inflammatory reactions. (6)

Drug treatments. Depending on the pathology diagnosed, certain treatments may be prescribed such as anti-inflammatory drugs.

Thrombolyse. Used during strokes, this treatment consists of breaking up the thrombi, or blood clots, with the help of drugs. (4)

Surgical treatment. Depending on the type of pathology diagnosed, surgery may be performed.

Chemotherapy, radiotherapy. Depending on the stage of the tumor, these treatments can be implemented.

Physical examination. First, a clinical examination is performed in order to observe and assess the symptoms perceived by the patient.

Medical imaging examination. In order to assess brainstem damage, a cerebral and spinal CT scan or a cerebral MRI can in particular be performed.

Biopsy. This examination consists of a sample of cells.

Lumbar puncture. This exam allows the cerebrospinal fluid to be analyzed.

The function of the corpus callosum was unveiled in the 50s thanks to the work of Ronald Myers and Roger Sperry at the California Institute of Technology (7). Their studies on the corpus callosum section in cats revealed no effect on behavior while learning faculty and perception appeared to be altered (1).