The corpus callosum connects the hemispheres of the brain. It runs transversely and consists of a large number of fibers. It is also called the bar.
What is the corpus callosum?
The corpus callosum is medically referred to as the commissura magna. In addition, it is also titled the bar. It is composed of over 200 million nerve fibers. In the cerebrum, efferent nerve fibers are distinguished from afferent ones. The cerebrum is called the telencephalon. It forms the largest part of the human brain. The cerebrum is part of the central nervous system and has two hemispheres. Thus, it is divided into the right and left hemispheres. The cerebrum is responsible for processing many thought and action processes. In it there are different pathway systems consisting of fibers. These are divided into three categories. These include the commissural fibers, the projection fibers, and the association fibers. The projection fibers connect the basal ganglia to the brainstem. The association fibers link individual areas of the same hemisphere. The corpus callosum forms the commissural fibers. These connect the areas of almost all parts of both hemispheres. The area of the primary auditory and visual cortex is excluded. Thus, the corpus callosum is responsible for allowing communication and information transfer between the two hemispheres of the brain to function.
Anatomy and structure
The corpus callosum has a curved structure and is located at the level of the temporal lobes. Viewed from above, it is in the middle of the head and runs along the longitudinal cerebral fissure. It forms the roof of the two lateral ventricles. The commissural fibers contained within it are double-stranded. The corpus callosum is divided into three sections. The frontal section is the bar knee or genu. The middle section is called the bar trunk or truncus. The posterior section represents the beam bulge or splenium. Below the genu, the corpus callosum runs out as a thin rostrum. The fibers connecting both frontal lobes are called the forceps frontalis or forceps minor. The fibers connecting both occipital lobes are the forceps occipitalis or forceps major. The corpus callosum connects the cortical areas with the identical tasks of the respective hemispheres. The posterior and anterior fibers of the corpus callosum are U-shaped. The posterior surface of the bar is called the dorsal surface. This is covered by a thin gray coating. It is called the indusium griseum. It is located in the cortical limbic areas.
Function and tasks
The corpus callosum performs an important function in connecting the two hemispheres of the brain. The commissural system located in it has the important task of transmitting information from both hemispheres. The right occipital lobe processes the visual information of the left visual field. Similarly, the left occipital lobe processes visual input from the right visual field. The corpus callosum allows both occipital lobes to exchange what they see of the entire visual field via a secondary communication pathway. The same is true for all other receptive and motor centers in the cortex of the cerebrum. Without the corpus callosum, this exchange would not occur. There is coordination of information from the respective hemispheres of the brain. The commissural fibers of the corpus callosum run both homotopically and heterotopically. Thus, the areas of the cortex are connected symmetrically as well as asymmetrically. This allows individual processes of information processing in the cerebrum to be divided into different regions and later reassembled as well as coordinated with each other. This means that objects seen through the left side of the face or felt with the hands can only be named through the functional activity of the corpus callosum. The reason for this is that the associated sensory information is processed and interpreted in the right hemisphere of the brain. In the left hemisphere, however, the naming of the sensed object is done by the language centers. The connection of the cerebral hemispheres with each other has an important meaning in the verbal-musical as well as the verbal-analytical information transfer as well as processing. Thus, the task field of the bar goes far beyond a purely functional merging of the hemispheres.
Diseases
Lesions in the corpus callosum area lead to defective processing of information received in the respective hemispheres of the brain. Objects palpated or seen might not be recognized or named. The information received through the senses can no longer be fully processed and assembled in the individual sensorimotor areas. This leads to life-altering changes and has a major impact on coping with everyday life. Clinically, the corpus callosum plays an important role in disorders such as epilepsy. Before there were good medications that are used today in the treatment of epilepsy, surgery was used to surgically cut the corpus callosum. This surgical procedure is called callosotomy or split-brain surgery. Today, it is only performed in isolated cases of very severe forms of epilepsy. By cutting the corpus callosum, physicians want to prevent the pathogen from spreading from one half of the brain to the other. Consequently, severing the interface of both hemispheres is intended to prevent the disease from worsening. In addition to conditions such as severe epilepsy, the surgical procedure has often been performed in the past following severe fall seizures. The use of this method has been significantly reduced in these patients as well. Because the cognitive impairment of such an operation is immense, the method is considered highly controversial, although it has not been fully abandoned to date.
