Postcentral gyrus: characteristics and functions of this brain area.

A summary of the physical and functional characteristics of this brain gyrus.

The cortex of the human brain has numerous gyri and convolutions that give it its particular wrinkled appearance. Among these folds we can find the postcentral gyrus, a structure located in the parietal lobe that contains the primary somatosensory cortex, responsible for processing somatic sensations (such as touch, temperature or pain).

In this article we explain what the postcentral gyrus is and where it is located, what the main functions of the somatosensory system it houses are and what kind of disorders originate when damage occurs in this brain structure.

Postcentral gyrus: definition and neuroanatomical localization

The postcentral gyrus is a brain gyrus located in the lateral parietal lobe. It is part of the so-called primary somatosensory cortex, as it receives most of the thalamocortical nerve projections (connecting the thalamus with the cerebral cortex) from the sensory input systems.

The nerve projections to the postcentral gyrus comprise thalamocortical fibers from the ventral posteromedial and ventral posterolateral nuclei of the thalamus. These nuclei transmit somatosensory signals from both sides of the contralateral face and body, respectively.

Structurally, the postcentral gyrus is bounded by the medial longitudinal fissure (towards the center), by the central sulcus (in front), by the caudal postcentral sulcus (behind) and by the inferior lateral sulcus (below). Although the somatosensory cortex was initially defined as part of Brodmann's areas 1, 2 and 3, it is now considered that this area should only be considered as part of area 3.

The human body is represented by a somatotopic map in the primary somatosensory cortex which is located in the postcentral gyrus, with a homunculus-like pattern.. This figure is often used to describe the distorted human figure, reflecting the relative sensory space occupied by each body part in the cerebral cortex.

Certain body areas are more sensitive and overrepresented in the sensory homunculus of the somatosensory cortex, such as the lips, hands, feet and sexual organs. The leg and genitals are represented in the medial aspect of the cortex, and the rest of the body and the head in the lateral aspect.

Functions

The postcentral gyrus, as we have advanced, is a brain gyrus in which we can locate the primary somatosensory cortex, which is in charge of functions such as the localization of touch, changes in body temperature or vibrations; the voluntary movement of the hands; the swallowing of the mouth, the swallowing of the mouth, the swallowing of the mouthThe primary somatosensory cortex is responsible for functions such as the localization of touch, changes in body temperature or vibrations; voluntary hand movements; intentional swallowing; taste perception and tongue movements, among others.

The primary somatosensory cortex belongs to the somatosensory system, an indispensable part of the sensory nervous system and whose receptor cells work on the basis of heat stimuli or nociceptive stimuli (related to pain). These can be thermoreceptors, nociceptors, mechanoreceptors or chemoreceptors, depending on the information they transmit.

Association fibers from the primary somatosensory cortex project to the white matter of the parietal lobe and connect the postcentral gyrus with the somatosensory association areas that integrate touch and conscious proprioception (the sense that allows us to locate and move in space properly) with other sensory modalities. (the sense that allows us to locate and move in space properly) with other sensory modalities.

Research with phobic subjects has found that cerebral Blood flow increases in the somatosensory cortex (and in other areas, such as the frontal, cingulate, insular and temporal cortex) when participants are presented with the object that provokes the specific phobia, with a predominance of sensations before images in which touch was stimulated.

On the other hand, several studies have shown that the upper part of the postcentral gyrus is activated in response to air puffs directed at various parts of the face. This appears to be a region whose function is coding the location of objects close to the face, or those that come into contact with the face, and may be used in the breastfeeding period.and it is possible that it may be used in the breastfeeding period.

Related disorders

Lesions in the primary somatosensory cortex which houses the postcentral gyrus include characteristic symptoms such as: agraphesthesia, a sensory disorder that causes difficulties in recognizing figures, numbers and letters traced on the skin and palm of the hand; decreased or loss of vibration sensation; and reduced or loss of proprioception and fine touch.

Damage to the postcentral gyrus often results in somatosensory disturbances on the affected contralateral side, and may also include a loss of nociception (the emission of pain signals) and thermoception (the reception of information about skin and body temperature), as well as postural sensitivity.

There are several neurodegenerative disorders and diseases that include impairment of somatosensory functions due to involvement of the postcentral gyrus and other related structures.. Here are some examples:

1. corticobasal degeneration.

Corticobasal degeneration is a neurodegenerative disease characterized by a progressive and asymmetric picture of extrapyramidal (rigidity, dystonia, tremor) and cortical (apraxia, cortical sensory disturbances, etc.) symptoms.

Patients suffering from this condition show cerebral atrophy involving neuronal nuclei in the precentral and postcentral gyrus, with involvement of primary and secondary somatosensory cortex.with involvement of the primary and secondary somatosensory cortex.

2. Somatosensory seizures

Somatosensory seizures or auras are the result of a nerve discharge affecting the postcentral gyrus. Contralateral manifestations involving more or less extensive parts of the middle of the body may include: tingling sensations, numbness, paresthesias or pain..

3. Neglect syndromes

Lesions in the non-dominant parietal lobe (usually the right) may cause hemineglect, in which the opposite side of the environment is ignored despite normal vision.

Some patients with these disorders may develop associated neurological deficits, such as paralysis of the extremities, although they are usually unaware of theiralthough they are often unaware of their deficits and may deny them (anosognosia).

4. Proprioceptive deficits

Damage to the postcentral gyrus of the parietal lobe, dorsal columns or dorsal root ganglia may result in loss of proprioception, astereognosia (inability to identify objects by touch), loss of vibratory sensations and loss of two-point discrimination in the trunk or limbs.

When the lesion occurs below the level of the medulla, the loss of proprioception is ipsilateral (on the same side). (on the same side). If it occurs above the level of cord decussation, the loss occurs on the side contralateral to the site of injury.

Bibliographic references:

• Martin, J.H. (2014). Neuroanatomia-: Texto e Atlas. AMGH Editora.
• Pain perception: is there a role for primary somatosensory cortex?. Proceedings of the National Academy of Sciences, 96(14), pp. 7705 - 7709.
• Snell, R.S. (2007). Clinical neuroanatomy. Ed. Médica Panamericana.