Corpus callosum of the brain: structure and functions

Let’s think for a moment of a human brain. It is a structure of great complexity in which the existence of two clearly differentiated parts is perceived, the two cerebral hemispheres.

We also know that each of these hemispheres has more specialized functions in different aspectsFor example, finding speech in the left hemisphere (usually) or seeing that while the right hemisphere is more holistic or global, the left is more logical and analytical. However, these two hemispheres are not loose and separate from each other, but at some point in the anatomy of the brain, it is possible to find a point of union. This point of union is the so-called corpus callosum.

What is the corpus callosum?

The main set of nerve fibers that connects the two brain hemispheres is called the corpus callosum. This structure is mainly composed of neural axons coated with myelin, so that they are part of the white matter of the brain. Within white matter, the corpus callosum is considered to be an interhemispheric commissure because it connects and exchanges information between the structures of different hemispheres. In the human brain, there are other interhemispheric commissures, but they are much smaller than the corpus callosum.

This structure is located in the midline of the brain, located at the bottom of the interhemispheric slit, and is mostly hidden from external observation by being partially covered by the cortex. It is shaped like a leaf or a comma, with different parts that connect different parts of the brain.

The areas connected by this brain structure are mostly cortical areas, with a few exceptions. In general, subcortical structures communicated with other structures and commissures.

Parts of the corpus callosum

Although the corpus callosum is considered to be a single structure, it is traditionally divided into several parts. More precisely, the corpus callosum could be divided into four sections.

1. Top of the podium

Located in the lower front part of the corpus callosum, it is the most anterior part of this structure. It arises from the terminal leaf and connects to the optic chiasm.

2. Knee or knee

This is the part of the corpus callosum that curves inward in the brain, leading earlier to the frontal lobes to form smaller pincers. The fibers of this part of the corpus callosum they connect the prefrontal cortices of the two hemispheres, allowing the integration of their information.

3. Cos

After the knee or the knee, it is the body, which eventually thickens in the back. It connects with the septum and the trineThis in turn is an important connecting structure between regions of the such as the thalamus, the hippocampus, and other areas of the limbic system.

4.splenium or roller

The posterior and final part of the corpus callosum is formed by the fibers that compose them end up being associated with other projecting and associative fibers. It connects to the occipital lobe to form the larger forceps, and also it binds to the lateral ventricle to the point of forming one of its lower walls. It also connects to the pineal gland and the habenular commissure (which connects the habenular nuclei of the two hemispheres).

Functions of this part of the brain

The main function of the corpus callosum is to transmit information from one hemisphere to another, Allow interhemispheric communication. In this way, the fact that the functions of each of the hemispheres are partly different does not prevent them from acting as an integrated whole, allowing the precise execution of the different processes and actions carried out by human beings.

In this sense too it is linked to learning and processing information, By joining and acting as a link between the different nuclei of the brain. On the other hand, if for example part of a cerebral hemisphere is damaged, thanks to the corpus callosum the opposite hemisphere can take over these functions which are neglected.

In addition, some studies show that in addition to this function, the corpus callosum it also influences vision, especially eye movement, Be transmitted through it information about the muscles of the eye. This is natural, because in eye movements the coordination between the two hemicoses is crucial, in this case the eyes.

What happens when it is severed?

The corpus callosum is an important structure for integrating the information received and processed by the two cerebral hemispheres. Although the absence of connection between the hemispheres at the level of the corpus callosum does not mean a complete loss of functionality (since if it is the main interhemispheric commissure, it is not the only), The total or partial disconnection of the cerebral hemispheres can imply a significant handicap for the accomplishment of various activities.

Among other things, this kind of disconnection between parts of the brain can give way to what is called callus disconnection syndrome.

In this syndrome, we have seen how patients with a divided brain (that is to say who have a disconnection between the two hemispheres) showed difficulties such as lack of coordination, repetition or persistence in performing sequenced activities like combing, feeding or dressing, sometimes performing the same action twice due to lack of motor integration.

too much significantly hinders the learning and retention of new information not being able to coordinate information correctly (although this does not make it impossible, requires a lot more effort than usual), as well as can cause alexia (inability to read) and stapling (inability to write).

In addition, at the sensory level, they can produce significant alterations. For example, it has been shown that subsequent damage to the corpus callosum can cause severe difficulty in distinguishing somatic stimuli, Causing somatic agnosia or lack of recognition of tactile stimuli. Memory and language problems are also common.

Callosotomy: when sectioning the corpus callosum can be good

Despite the disadvantages of performing this type of surgery, in the presence of certain very serious disorders, division of the corpus callosum or callosotomy has been evaluated and successfully applied. for medical purposes, as a minor ailment.

The most typical example is that of resistant epilepsy, in which the sectioning of parts of the corpus callosum is used as a method to reduce severe epileptic seizures, preventing epileptoid impulses from traveling from one hemisphere to the other. . Despite the problems it can cause on its own, callosotomy increases the quality of life of these patients, as the difficulties it can cause are less than those caused by continuing seizures, thereby reducing the risk of death and quality of life can improve.

On the other hand, over time, it is possible for the brain to reorganize itself to allow mental processes that, in the first few weeks after surgery, seemed to be eliminated or severely damaged, although recovery is usually not complete. .

Conditions that affect the corpus callosum

It has been stated above that division of the corpus callosum may have limiting effects, although its severing may sometimes be considered due to improved symptomatology of certain disorders.

however, that the corpus callosum is cut or damaged can happen accidentally or naturallyThere are several diseases that can affect this area of ​​the brain. Some of these changes may occur in the following cases.

1. Cranioencephalic trauma

In the event of a blow or trauma, the corpus callosum can be easily damaged mainly by due to its high consistency and density. usually a tear of the substance occurs, Or diffuse axonal damage as a result of the counterattack against the bones of the skull. If we are talking about point-focused effects, the greatest impact usually occurs in the splenium.

2. Strokes

Although this is not common due to bilateral irrigation that has the corpus callosum, it is possible to find cases in which hemorrhaging or ischemia causes alteration of the white matter of the corpus callosum. In this way, alterations in blood flow are able to virtually cut off the communication between the two hemispheres that takes place in the corpus callosum, without the need for a solid element to come into contact with this part of the brain and break it. .

3. Demyelinating disorders

Being a structure composed of white matter, covered with myelin, disorders such as multiple sclerosis greatly affect the corpus callosum. This type of disorder causes the messages sent by the brain to not be sent as efficiently or even many neurons die, so in the corpus callosum it causes the perceptions and functionality of the two hemispheres to not easily integrate. Thus, mental processes involving regions on either side of the brain are severely affected or cannot be performed directly.

4. Brain tumors

While its compaction means that in general there are not many tumors that affect the corpus callosum some major attacks such as lymphoma or polymorphic glioblastoma, Which is usually found in white matter, if they can infiltrate affect that particular structure and cause severe damage or “strangle” by the pressure exerted by the growth of cancerous parts.

In the case of glioblastoma, it usually produces a typical butterfly-shaped pattern with a greater affectation of the central area.

5. Malformations

Although it is not very common, it is possible to find deformities in some subjects that cause them to have a lower number of connections than usual from birth. Other types of birth defects can make it easier to rupture (And subsequent bleeding) from blood vessels in the brain, which can also affect the corpus callosum.

Bibliographical references:

  • Bishop, KM; Wahlsten, D. (1997). Sexual differences in the human corpus callosum: myth or reality ?. Neuroscience and reviews of biological behavior. 21 (5): 581-601.
  • Hofer, S .; Frahm, J. (2006). Revised topography of the human corpus callosum: complete fiber tractography using diffusion tensor magnetic resonance imaging. NeuroImage. 32 (3): 989-994.
  • Kandel, ER; Schwartz, JH and Jessell, TM (2001). Principles of neuroscience. Fourth edition. McGraw-Hill Inter-American. Madrid.
  • Mantilla, DL; Nariño, D .; Acevedo, JC; Berbeo, ME and Fox, OF (2011) Callosotomy in the treatment of resistant epilepsy. Bogota Medical University, 52 (4): 431-439.
  • Peña-Casanova, J. (2007). Behavioral neurology and neuropsychology. Pan American Medical Editorial.
  • Witelson, S. (1985). The brain connection: the corpus callosum is larger on the left. Science. 229 (4714): 665-8.

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