CORPUS CALLOSUM: ANATOMY, FUNCTION, INJURIES, AGENESIS - NEUROPSYCHOLOGY - 2025

The corpus callosum is the largest bundle of nerve fibers in the brain. It constitutes the interhemispheric commissure that allows to relate the analogous territories of the cerebral hemispheres. Its main function is to communicate the right hemisphere with the left hemisphere of the brain, so that both parties work together and in a complementary way.

It is a fundamental region of the brain, so the injury or malformation of the corpus callosum causes multiple alterations both in the functioning and in the intelligence of the person.

In this article, the anatomical and functional characteristics of the corpus callosum are reviewed, developmental properties are reviewed, and diseases related to this brain structure are discussed.

Anatomy of the corpus callosum

The corpus callosum is a sheet of white matter, which forms a quadrilateral area and is located transversely from one hemisphere to another. The result is an association system that brings together the two halves of the brain through the connection of non-symmetrical points in the cortex.

Laterally it draws an arch of inferior concavity, which covers the optestriate nuclei and the ventricular cavities. Its posterior end is voluminous and constitutes the "bump" of the corpus callosum.

The lower end is flexed downward and is called the "knee." It ends through a sharp end known as a spike. Its length on the upper face is between 7 and 8 centimeters, and on the lower face between 6 and 7 centimeters.

The width of the corpus callosum on the upper face is about two centimeters, while on the lower face it reaches 3-4 centimeters. The corpus callosum rim is about 15 millimeters long.

The corpus callosum is made up of approximately 200 million axons that come mainly from the cells of the pyramids of layers II and III of the cerebral cortex.

Parts

Corpus callosum in orange

The corpus callosum has a large number of structures. However, from the anatomical point of view, it is made up of three main parts: the body or trunk, the bun, and the knee.

Each of these portions refers to a different region of the corpus callosum, and has certain characteristics.

Body

The body or trunk of the corpus callosum constitutes the upper face of the structure. It is convex in shape at the back, and is flat or slightly concave in the transverse region.

In the body there is a longitudinal groove that is the vestige of the raphe of the corpus callosum. On each side of this groove are two small cords, known as longitudinal striae.

The longitudinal striae are linked to the middle tract by a thin veil of gray matter called indusium griseum. This gray veil is the continuation of the cerebral cortex of the corpus callosum gyrus.

The lower face of the body is convex in the transverse direction and has a concave shape in the anteroposterior direction. In the midline it has the septum lucidum, and from behind it contacts the transverse fibers of the trigone.

Impeller

The impeller constitutes the posterior end of the corpus callosum. It is a rounded area that appears formed by the folding of the corpus callosum on itself.

Between the impeller and the trigone is a cleft that communicates the hemispheres with the lateral ventricles.

Knee

Finally, knee is the name given to the anterior end of the corpus calli. It is the thinnest region and presents a downward and backward curve.

The knee is made up of reflected fibers that are continued downward by a sharp portion of the beak. On the underside, there are two whitish tracts called peduncles of the corpus callosum.

Development

The corpus callosum develops mainly during the prenatal period, following an anteroposterior pattern. That is, the rostrum area begins to develop and ends at the knee.

Most authors who have examined its structure and development affirm that the corpus callosum has 7 subareas with different functional anatomical significance. These are:

1. Rostrum or peak: corresponds to the orbital area of ​​the prefrontal lobe and the inferior premotor cortex.
2. Knee: it is related to the rest of the prefrontal lobe.
3. Rostral body: establishes connections between the premotor and supplementary zones.
4. Medial anterior body r: it is formed by association fibers of the motor areas and the fraction.
5. Posterior medial body: receives fibers from the superior temporal and parietal lobes.
6. Isthmus: it is formed by the association fibers of the upper part of the temporal lobe.
7. Impeller: it is formed by the connecting fibers of the lower part of the temporal lobe and the cortex of the occipital lobes.

The development of the corpus callosum begins approximately during the eighth week of gestation, through the formation of the knee, followed by the body and the posterior part.

Thus, at the time of birth, all subareas of the corpus callosum have already developed. However, its myelination continues into childhood or even later in life.

In this sense, several studies point out that the corpus callosum experiences a linear increase in its sagittal area between 4 and 18 years of life.

The reason for the postnatal maturation of the corpus callosum is not entirely clear. However, it is postulated that it may be due to myelination of fibers, which occurs during childhood and adolescence.

The myelinated axons of the neurons of the corpus callosum allow rapid propagation of neural impulses and are a requirement for the acquisition of cognitive, emotional, behavioral, and motor functions at various stages of maturation.

Maturation and development of the corpus callosum

Corpus callosum in red

Several studies have focused on analyzing which physiological variables, maturational changes, and emotional and behavioral modifications are related to the development of the corpus callosum.

In this sense, today there is an abundant literature on the effects and functions of the maturation of the different regions of this brain structure.

The most important brain processes are:

Striking physiological variables during development

The dynamic activity of brain development takes place in the womb. However, the changes continue during the first years of life.

Hemispheric axons are the last to myelinate. In this sense, the primary sensory and motor areas are myelinated before the frontal and parietal association areas.

Likewise, with growth, a decrease in the number of synapses and an increase in the complexity of dendritic arborizations is observed. Synaptic density remains until four years of age, at which point it begins to decrease due to brain plasticity.

Behavioral and neurobiological changes

The connoted changes in the corpus callosum are related to a series of psychological and neurobiological variables. Specifically, it has been shown how the thickening of the knee and the buckle is positively related to the following elements:

• Extension and turning of the head.
• Voluntary control and search for objects presented in the visual field during the first three months of life.
• Ability to pick up objects with both hands and crawl in the 9 months of life.
• Development of sensory functions such as binocular vision, or visual awareness and accommodation.
• Appearance of prelinguistic verbal language during the first twelve months of life.

Behavioral changes between the first and fourth year of life

Continued growth of the corpus callosum during later stages is also associated with changes in behavior in children. Specifically, these variables usually appear between 2 and 3 years of life.

• Ability to climb and descend stairs with two feet.
• Ability to climb stairs with one foot, ride a tricycle and dress.
• Development of the first linguistic level: pronunciation of two-word sentences, marking parts of the body, use of questions and development of well-structured sentences.
• Presence of auditory asymmetry: the left hemisphere developed faster in the analysis of verbal information and the right in the handling of non-verbal information.

Behavioral changes between the fourth and seventh year of life

The enlargement of the corpus callosum continues throughout childhood. In this sense, a series of changes associated with the maturation of the corpus callosum up to seven years have been connoted.

• Development of the ability to jump and tie the shoelaces.
• Acquisition of the first linguistic level: say the age, repeat four digits and name colors.
• Setting the manual preference.
• Development of visual recognition and reading comprehension.

Function

The most important function of the corpus callosum is to facilitate the communication process between the hemispheres of the brain. In fact, without the corpus callosum functioning, the connection between both parts would be impossible.

The functions of the right hemisphere differ from those of the left hemisphere, so it is necessary to connect both regions to facilitate the functioning of the nervous system as a single mechanism.

In this way, this function is performed by the corpus callosum, which is why this structure is vital for exchange, acting as a bridge between both hemispheres and transmitting information from one to the other.

Likewise, the corpus callosum also works in assigning tasks to any of the hemispheres of the brain based on its programming. In children, it plays an important role in the lateralization process.

On the other hand, several studies indicate how this structure actively participates in the movement of the eyes. The corpus callosum collects information about the muscles of the eye and the retina, and sends it to the areas of the brain where eye movements are processed.

Corpus callosum injuries

Injuries to the corpus callosum cause a wide range of alterations both in physical functioning and in people's cognitive, behavioral and emotional development.

At present, multiple pathologies have been detected that can affect the corpus callosum. In general, these are classified based on their pathogenesis.

Thus, the pathologies of the corpus callosum can be divided into congenital, tumorous, inflammatory, demyelinating, vascular, endocrine, metabolic, infection and toxic.

Congenital diseases include agenesis, dysgensia, and prenatal noxa atrophy. Tumor pathologies present gliomas, lymphomas, asotrictomas, interventricular tumor lesions and metastases that affect the corpus callosum.

For their part, inflammatory-demyelinating pathologies include multiple sclerosis, Susac syndrome, acute disseminated encephalomyelitis and progressive multifocal leukoencephalopathy.

Vascular diseases of the corpus callosum can be caused by heart attacks, periventricular leukomalacia, arterio-venous malformations, or trauma that affect the anatomy of the brain structure.

Endocrine metabolic pathologies include metachromatic leukodystrophy, adrenoleukodystrophy, inherited metabolic disorders, and thiamine deficiency.

Finally, infection of the parenchyma and toxic pathologies such as marchiafava-bignami, disseminated necrotizing leukoencephalopathy or radiation changes, can also alter the function and structure of the corpus callosum.

Agenesis of the corpus callosum

Although the diseases that can affect the corpus callosum are numerous, the most important is agenesis of the corpus callosum (ACC). It is about one of the most frequent malformations of the central nervous system and is characterized by the lack of formation of the corpus callosum.

This pathology originates due to an alteration of embryonic development and can cause both the partial and total lack of the fiber bundle that is responsible for uniting the hemispheres of the brain.

ACC can occur as an isolated defect or in combination with other brain abnormalities such as the Arnold-Chiari malformation, Dandy-Walker syndrome, or Andermann syndrome.

The alterations caused by this disease are variable, and can be subtle or mild to serious and very disabling. The magnitude of the alteration depends mainly on the anomalies associated with ACC.

In general, people with ACC have normal intelligence with a slight compromise in skills that require matching visual patterns.

However, in some cases, ACC can cause significant intellectual retardation, seizures, hydrocephalus, and spasticity, among other disorders.

References

1. Aboitiz, F., Sheibel, A., Fisher, R., & Zaidel, E. (1992). Fiber composition of the human corpus callosum. Brain Research, 598, 143-153.
2. Barkovich AJ. Anomalies of the corpus callosum. In Barkovich J, ed. Pediatric neuroimaging. Philadelphia: Lippincott Williams & Wilkins; 2000. p. 254-65.
3. Frederiksen, KS, Garde, E., Skimminge, A., Barkhof, F., Scheltens, P., Van Straaten, EC, Fazekas, F., & Baezner, H. (2011). Corpus Callosum Tissue Loss and Development of Motor and Global Cognitive Impairment: The LADIS Study. Dementia and Geriatric Cognitive Disorders, 32 (4), 279–286.
4. Goodyear PW, Bannister CM, Russell S, Rimmer S. Outcome in prenatally diagnosed fetal agenesis of the corpus callosum. Fetal Diagn Ther 2001; 16: 139-45.
5. Jang, JJ, & Lee, KH (2010). Transient splenial lesion of the corpus callosum in a case of benign convulsion associated with rotaviral gastroenteritis. Korean Journal of Pediatrics, 53 (9).
6. Kosugi, T., Isoda, H., Imai, M., & Sakahara, H. (2004). Reversible focal splenial lesion of the corpus callosum on MR images in a patient with malnutrition. Magnetic Resonance in Medical Sciences, 3 (4), 211-214.