What happens if the corpus callosum is cut?

In this article we are going to answer the question ‘’What happens if the corpus callosum is cut?’’ We will explain what the corpus callosum is, what its parts and functions are and what would happen if this part of the brain is cut off.

What happens if the corpus callosum is cut?

Cutting the corpus callosum helps prevent the spread of seizures from hemisphere to hemisphere.

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

We also know that each of these hemispheres has some more specialized functions in different aspects, for example finding speech in the left hemisphere (generally) or having seen 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 separated from each other, but at some point in the anatomy of the brain, it is possible to find a point of union. Said point of attachment is the so-called corpus callosum.

What is the corpus callosum?

The corpus callosum is the main set of nerve fibers that connects both hemispheres of the brain. This structure is mainly made up of neuronal axons coated with myelin, making them part of the white matter of the brain.

Within the white matter, the corpus callosum is considered an interhemispheric commissure, since it connects and exchanges information between structures in the different hemispheres.

In the human brain there are other interhemispheric commissures, but they are much smaller than the corpus callosum.

This structure is found in the midline of the brain, located at the bottom of the interhemispheric fissure, and for the most part hidden from external observation as it is partially covered by the cortex. It is shaped like a leaf or comma, having different parts that connect different parts of the brain.

The areas connected by this structure of the brain are mostly cortical areas, although with some exceptions. Usually the subcortical structures communicating with other structures and commissures.

Parts of the corpus callosum

Although the corpus callosum is considered a single structure, it has traditionally been divided into several parts. Specifically, the corpus callosum could be divided into the following four sections.

1. Pico or rostrum

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

2. Genu or knee

It is the part of the corpus callosum that curves into the brain, moving before the frontal lobes to form minor forceps. The fibers of this part of the corpus callosum connect the prefrontal cortices of the two hemispheres, allowing their information to be integrated.

3. Body

After the genu or knee, is the body, which ends up thickening at the back. It connects with the septum and the trigone, this in turn being an important connecting structure between regions of the brain, such as the thalamus, the hippocampus and other areas of the limbic system.

4. Splenium or bun

The most posterior and final part of the corpus callosum is formed by the fibers of which they consist, which end up associating with other projection and associative fibers. It connects to the occipital lobe to form the greater forceps, and it also connects to the lateral ventricle to the point of forming one of its lower walls. 

It also connects with the pineal gland and the habenular commissure (which connects the habenular nuclei of both hemispheres).

Functions of the corpus callosum

This structure is involved in various functions of the brain, being essential for them to perform correctly. Some are as follows:

Binocular vision

The mechanism called stereopsis is the one that is responsible for the depth of our vision. That is, thanks to stereopsis we can distinguish distances in our environment.

A small part of this structure participates in this stereopsis. This occurs since in our optic chiasm there is a decussation of fibers. That is, the fibers cross: what makes each hemisphere reach an “input” from the opposite visual field.

Thus, the corpus callosum ensures that there is a good connection between the two hemispheres in terms of the information that comes from each eye.

Eye movements

For eye movements to occur, both hemispheres of the brain must work at the same time in certain areas. Areas such as prefrontals and parietals are responsible for the proper motor programming and visual-spatial attention.

These processes are necessary when moving the eyes. That is why, in order to have visual tracking and saccades, we need the corpus callosum to take care of communicating these areas well.

Visual perception

It seems that interhemispheric communication is key in visual integration. A 2015 study conducted by researchers in Poland found that there is a direct relationship between poor visual perception test performance and low corpus callosum volume. Other studies also show a relationship between the volume of the corpus callosum and visual attention.

What happens when it is sectioned?

The corpus callosum is an important structure when it comes to integrating the information received and processed by both hemispheres of the brain.

Although the absence of connection between hemispheres at the level of the corpus callosum does not imply a complete loss of functionality (since although it is the main interhemispheric commissure, it is not the only one), the total or partial disconnection of the cerebral hemispheres can represent an important handicap for carrying out various activities.

Among other things, this kind of disconnection between parts of the brain can lead to what is known as callosal disconnection syndrome.

In this syndrome, it has been seen how patients with divided brain (that is, who present a disconnection between both hemispheres) have shown difficulties such as incoordination, repetition or perseverance when carrying out sequenced activities such as combing, eating or dressing , sometimes performing the same action twice due to lack of motor integration.

It also greatly hinders the learning and retention of new information by not being able to coordinate the information correctly (although it does not make it impossible, it requires a much greater effort than usual), as well as it can cause alexia (inability to read) and agrafia (inability to write).

In addition, at a sensory level, significant alterations can occur.

For example, it has been shown that subsequent lesions of the corpus callosum can cause severe difficulties in discriminating between somatic stimuli, causing somatic agnosias or lack of recognition from tactile stimuli. Memory and language problems are also common.

Callosotomy: when sectioning the corpus callosum can be good

Despite the disadvantages that this type of surgical intervention may entail, in the presence of some very serious disorders, division of the corpus callosum or callosotomy for medical purposes has been evaluated and successfully applied, as a lesser evil.

The most typical example is that of resistant epilepsy, in which the sectioning of parts of the corpus callosum is used as a method of reducing severe seizures, preventing epileptoid impulses from traveling from one hemisphere to another.

Despite the problems that it can cause by itself, callosotomy increases the quality of life of these patients, because the difficulties it can cause are less than those caused by continuous seizures, thereby reducing the risk of death and quality of life may improve.

On the other hand, over time it is possible that the brain reorganizes to allow mental processes that during the first weeks after the operation seemed eliminated or seriously damaged, although recovery is not usually complete.

Conditions that affect the corpus callosum

It has been previously indicated that the division of the corpus callosum can have limiting effects, although its section can sometimes be considered by virtue of improving the symptoms of a disorder.

However, that the corpus callosum is cut or damaged can occur in an accidental or natural way, there are multiple diseases that can affect this area of ​​the brain. Some of these alterations can occur from the following.

1. Head trauma

In the event of a blow or trauma, the corpus callosum can be easily damaged mainly due to its great consistency and density. Generally, there is a tear of the substance, or diffuse axonal damage as a consequence of the blow-back impact against the bones of the skull. If we talk about effects focused on one point, the greatest affectation is usually in the splenium.

2. Stroke

Although it is not frequent due to the bilateral irrigation of the corpus callosum, it is possible to find cases in which hemorrhages or ischemias produce an affectation of the white matter of the corpus callosum.

In this way, alterations in blood flow are capable of practically cutting 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 formed by white matter, covered with myelin, disorders such as multiple sclerosis affect the corpus callosum to a great extent.

This type of disorder causes that the messages sent by the brain are not sent in such an efficient way or even that many neurons die, with which in the corpus callosum it is caused that the perceptions and functionalities of both hemispheres cannot be easily integrated.

In this way, mental processes that involve regions on both sides of the brain are greatly affected, or cannot be carried out directly.

4. Brain tumors

Although its compaction means that in general there are not many tumors that affect the corpus callosum, some of great aggressiveness such as lymphoma or glioblastoma multiforme, which are usually located in the white matter, if they can infiltrate affect this specific structure and cause serious damage or or “strangle” it by the pressure exerted by the growth of cancerous parts.

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

5. Malformations

Although not very frequent, it is possible to find malformations in some subjects that cause them to have fewer connections than usual from birth. 

Other types of congenital malformations can make it easy to break (and consequently bleed) of blood vessels in the brain, which can also affect the corpus callosum.

FAQS:  What happens if the corpus callosum is cut?

What will occur when the corpus callosum is severed?

A procedure that severs (cuts) the corpus callosum, interrupting the spread of seizures from hemisphere to hemisphere, is a corpus callosotomy.

Why would the corpus callosum be cut?

In this process, in an attempt to restrict the spread of epileptic activity between the two halves of the brain, the corpus callosum is sliced through.

Can you live without a corpus callosum?

You can live with only one part of the corpus callosum.

What happens if you have a split brain?

Some patients with split brain have the ability to produce language in both hemispheres.

How does the corpus callosum affect behavior?

Typical symptoms include learning difficulties (especially language), intellectual disabilities, and behavioral problems such as emotional disorders, aggressiveness, attention deficit / hyperactivity, and autistic traits.

In this article we answered the question ‘’What happens if the corpus callosum is cut?’’ We explained what the corpus callosum is, what its parts and functions are and what would happen if this part of the brain is cut off.

If you have any questions or comments please let us know!

References

Bishop, K.M.; Wahlsten, D. (1997). Sex Differences in the Human Corpus Callosum: Myth or Reality?. Neuroscience & Biobehavioral Reviews. 21 (5): 581 – 601

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Hofer, S.; Frahm, J. (2006). Topography of the human corpus callosum revisited—Comprehensive fiber tractography usin

Witelson, S. (1985). The brain connection: The corpus callosum is larger in left-handers. Science. 229 (4714): 665–8.