He hard body Is the largest bundle of nerve fibers in the brain. It constitutes the interhemispheric commissure that allows to relate the similar 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 complementary.
It is a key region of the brain , So that the lesion or malformation of the corpus callosum causes multiple alterations in both the functioning and the intelligence of the person.
The present article reviews the anatomical and functional characteristics of the corpus callosum, reviews developmental properties and discusses diseases related to this cerebral structure.
Anatomy of the corpus callosum
The corpus callosum is a leaf of White matter , Which forms a quadrilateral area and is transversely stretched from one hemisphere to another.
It is a system of association that brings together the two halves of the brain through the connection of non-symmetrical points of the cortex.
Laterally, it draws an arc of inferior concavity, which covers the op- tressed nuclei and the ventricular cavities. Its posterior extremity is bulky and constitutes the"rump"of the corpus callosum.
The lower end flexes downward and is called the"knee." It ends through a sharp end known as a peak. Its length of the upper face is between 7 and 8 centimeters, and 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 rump of the corpus callosum has a length of one 15 millimeters.
The corpus callosum is formed by approximately 200 million axons that come mainly from the cells of the pyramids of layers II and III of the cerebral cortex.
Structure
The corpus callosum has a large number of structures. However, from the anatomical point of view it is composed of three main parts: the body or trunk, the impeller and the knee.
Each of these portions refers to a region other than the corpus callosum, and has certain characteristics.
Body
The body or trunk of the corpus callosum constitutes the upper face of the structure. It has a convex shape at the back, and is flat or slightly concave in the transverse region.
The body shows a longitudinal groove that results the vestige of the raphe of the corpus callosum. On each side of this groove are two small cords, known as longitudinal grooves.
The longitudinal striae are linked to the middle tract by a thin gray veil called Indusium griseum . This gray veil is the continuation of the cerebral cortex of the convoluted corpus callosum.
The lower face of the body is convex in transverse direction and has a concave shape in the anteroposterior direction. In the middle line has the septum lúcidum, and behind it contacts the transverse fibers of the trigone.
Rodete
The imput 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 recess that communicates the Hemispheres With the lateral ventricles.
Knee
Finally, the knee is the name that receives the anterior end of the callus body. It is the thinnest region and presents a downward and backward curve.
The knee is formed of reflected fibers which are continued downwards by a sharp portion of the beak. On the underside, there are two whitish tracts that are called peduncles of the corpus callosum.
Development
The corpus callosum develops primarily during the prenatal period, following an anteroposterior pattern. That is to say, it begins to develop the rostrum area and ends at the knee.
The majority of authors who have examined its structure and development affirm that the corpus callosum has 7 subareas with a different anatomical functional meaning. These are:
- Rostrum the Peak : Corresponds to the orbital area of the prefrontal lobe and the inferior premotor cortex.
- Knee : It is related to the rest of the prefrontal lobe.
- Rostral body : Establishes connections between premotor and supplementary zones.
- Medial body anterior R: is formed by fibers of association of the motor areas and the fraction.
- Posterior medial body : Receives fibers from the upper temporal lobes and parietal .
- Isthmus : Is formed by the association fibers of the upper part of the Temporal lobe .
- Rodete : It is formed by the connecting fibers of the inferior part of the temporal lobe and the crust 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 back.
Thus, at the time of birth all the subareas of the corpus callosum have already developed. However, their Myelination Continues during childhood or even more advanced ages.
In this sense, several studies indicate that the corpus callosum undergoes a linear increase of its sagittal area between 4 and 18 years of life.
The reason for 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 prerequisite for the acquisition of cognitive, emotional, behavioral and motor functions at various stages of maturation.
Maturation and development of the corpus callosum
Several studies have focused on analyzing what physiological variables, maturational changes and emotional and behavioral changes are related to the development of the corpus callosum.
In this sense, today there is an abundant literature on the effects and functions that the maturation of the different regions of this brain structure performs.
The most important brain processes are:
Striking physiological variables during development
The dynamic activity of brain development takes place in the uterus. However, the changes continue during the first years of life.
The hemispheric axons are the last to be myelinated. In this sense, the primary sensory and motor areas are myelinated before the frontal and parietal association areas.
Likewise, with growth, there is a decrease in the number of synapses and an increase in the complexity of dendritic arborizations. The synaptic density remains until the four years of life, at which point it begins to decrease due to the brain plasticity .
Behavioral and neurobiological changes
The changes noted in the corpus callosum are related to a number of psychological and neurobiological variables. Specifically, it has been demonstrated how thickening of the knee and the impeller is positively related to the following elements:
- Extension and turning of the head.
- Voluntary control and search of objects presented in the visual field during the first three months of life.
- Ability to grasp objects with both hands and crawl in the 9 months of life.
- Development of sensory functions such as binocular vision, or awareness and visual accommodation.
- Prelinguistic verbal language appearance during the first twelve months of life.
Behavioral changes between the first and fourth year of life
The continuous growth of the corpus callosum during later stages is also related to the appearance of changes in the behavior of children. Specifically, these variables usually appear between 2 and 3 years of life.
- Ability to go up and down stairs with two feet.
- Ability to climb stairs with one foot, ride a tricycle and get dressed.
- Development of the first linguistic level: pronunciation of two-word phrases, signaling of body parts, 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 nonverbal information.
Behavioral changes between the fourth and seventh year of life
The increase of the corpus callosum continues during childhood. In this sense, a series of changes associated with maturation of the corpus callosum up to seven years have been connoted.
- Development of the ability to jump and love the laces.
- Acquisition of the first linguistic level: say age, repeat four digits and call colors.
- Establishment of manual preference.
- Development of visual recognition and reading comprehension.
Function
The most important function of the corpus callosum is to facilitate the process of communication between the Hemispheres of the brain . In fact, without the functioning of the corpus callosum the connection between the two 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.
Thus, this function is performed by the corpus callosum, so this structure is vital for the exchange, acting as a bridge between both hemispheres and transmitting information from one to another.
Likewise, the corpus callosum also works on 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 retina, and sends it to the areas of the brain where eye movements are processed.
Corpus callosum lesions
Lesions in the corpus callosum cause a wide range of alterations in both physical functioning and in the cognitive, behavioral and emotional development of people.
At present, there are many pathologies that can affect the corpus callosum. In general, these are classified based on their etiopathogenesis.
Thus, the pathologies of the corpus callosum can be divided into congenital, tumor, inflammatory, demyelinating, vascular, endocrine, metabolic, infections and toxic.
Congenital diseases include agenesis, dysgenesis, and prenatal noxous atrophy. The tumor pathologies present gliomas, lymphomas, asotrictomas, interventricular tumor lesions and metastases that affect the corpus callosum.
On the other hand, the inflammatory-demyelinating pathologies are the multiple sclerosis , Susac's syndrome, disseminated acute encephalomyelitis and Leukoencephalopathy Progressive multifocal.
Vascular diseases of the corpus callosum may be caused by infarcts, periventricular leukomalacia, arteriovenous malformations or trauma that affect the anatomy of the brain structure.
Metabolic endocrine pathologies include metachromatic leukodystrophy, adrenoleukodystrophy, hereditary metabolic disorders, and Thiamine .
Finally, infection of the parenchyma and toxic pathologies such as marchiafava-bignami, disseminated necrotizing leukoencephalopathy, or radiation changes can also alter the functioning 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 the agenesis of the corpus callosum (ACC). It deals with one of the malformations of the Central Nervous System More frequent and is characterized by the lack of formation of the corpus callosum.
This pathology originates due to an alteration of the embryonic development and can cause both the partial lack and the total lack of the fiber bundle that is responsible for joining the hemispheres of the brain.
ACC can occur as an isolated defect or in combination of other brain abnormalities such as malformation and Arnold-Chiari, Dandy-Walker syndrome Or Andermann's syndrome.
The alterations caused by this disease are variable, being subtle or mild to severe and very disabling. The magnitude of the alteration depends largely on the abnormalities associated with the ACC.
In general, people with CCA have normal intelligence with a slight compromise of skills that need to relate visual patterns.
However, in some cases, the CCA may lead to significant intellectual retardation, Convulsions , Hydrocephalus And spasticiadad, among other alterations.
References
- Aboitiz, F., Sheibel, A., Fisher, R., & Zaidel, E. (1992). Fiber composition of the human corpus callosum. Brain Research, 598, 143-153.
- Barkovich AJ. Anomalies of the corpus callosum. In Barkovich J, ed. Pediatric neuroimaging. Philadelphia: Lippincott Williams & Wilkins; 2000. p. 254-65.
- Frederiksen, K. S., Garde, E., Skimminge, A., Barkhof, F., Scheltens, P., Van Straaten, E. C., 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.
- 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.
- Jang, J. J., & Lee, K.H. (2010). Transient splenial lesion of the corpus callosum in a case of benign convulsion associated with rotaviral gastroenteritis. Korean Journal of Pediatrics, 53 (9).
- 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.