Postcentral Gyrus: Characteristics And Functions Of This Area Of the Brain
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 is the postcentral gyrus and where is it located? What are the main functions of the somatosensory system it houses? and what type of disorders arise when damage occurs to this brain structure.
Postcentral gyrus: definition and neuroanatomical location
The postcentral gyrus is a cerebral gyrus located in the lateral parietal lobe It is part of the so-called primary somatosensory cortex, since it receives most of the thalamocortical nerve projections (which connect the thalamus with the cerebral cortex) from the sensory input systems.
Nerve projections to the postcentral gyrus They comprise the thalamocortical fibers of the ventral posteromedial and ventral posterolateral nuclei of the thalamus. These nuclei transmit somatosensory signals from both sides of the face and the contralateral body, respectively.
At a structural level, the postcentral gyrus is delimited 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 currently considered that this area should be considered only as part of area 3.
The human body is represented by a somatotopic map in the primary somatosensory cortex located in the postcentral gyrus, with a homunculus-like pattern This figure is usually used to describe the distorted human figure, so that the relative sensory space occupied by each of the body parts in the cerebral cortex is reflected.
Certain body areas are more sensitive and are overrepresented in the sensory homunculus of the somatosensory cortex, such as the lips, hands, feet, and sexual organs. The leg and genitals are represented on the medial aspect of the cortex, and the rest of the body and head on the lateral aspect.
Features
The postcentral gyrus, as we have advanced, is a gyrus of the brain in which we can locate the primary somatosensory cortex, which is responsible for functions such as localization of touch, changes in body temperature or vibrations ; of voluntary movement of the hands; 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 based on 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 ourselves and move in space appropriately) with other sensory modalities.
In research carried out with phobic subjects, it has been 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 they are presented with. It causes 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 encode the location of objects close to the face, or those that come into contact with it and it may be used during breastfeeding.
Related disorders
Lesions in the primary somatosensory cortex housing the postcentral gyrus include characteristic symptoms such as: agraphesthesia, a sensory disorder that causes difficulties in recognizing figures, numbers and letters drawn on the skin and palm of the hand; decreased or loss of vibration sensation; and reduction or loss of proprioception and fine touch.
Damage to the postcentral gyrus usually causes somatosensory alterations in the affected contralateral part, and may also include a loss of nociception (the emission of pain signals) and thermoception (the receipt of information about skin and body temperature). ), as well as postural sensitivity.
There are various neurodegenerative disorders and diseases that include an impairment of somatosensory functions due to involvement of the postcentral gyrus and other related structures Next, we will see some examples:
1. Corticobasal degeneration
Corticobasal degeneration is a neurodegenerative disease characterized by a progressive and asymmetrical picture of extrapyramidal symptoms (rigidity, dystonia, tremors) and cortical symptoms (apraxia, cortical sensory alterations, etc.).
Patients suffering from this condition show cerebral atrophy involving neuronal nuclei in the precentral and postcentral gyrus with involvement of the primary and secondary somatosensory cortex.
2. Somatosensory seizures
Somatosensory seizures or auras are the result of a nerve discharge that affects the postcentral gyrus. Contralateral manifestations involving more or less extensive parts of the middle of the body may include: sensations of tingling, numbness, paresthesia or pain
3. Negligence syndromes
Lesions in the nondominant parietal lobe (usually the right) can cause hemineglect, in which the opposite side of the environment is ignored despite normal vision.
Some patients with these disorders may develop associated neurological deficiencies, such as paralysis of the extremities although they are usually not aware of their deficits and may deny them (anosognosia).
4. Proprioceptive deficits
Damage to the postcentral gyrus of the parietal lobe, the dorsal columns, or the dorsal root ganglia can lead to a loss of proprioception, astereognosia (inability to identify objects by touch), loss of vibratory sensations, and loss of discrimination. of two points on the trunk or extremities.
When the injury occurs below the level of the spinal cord, the loss of proprioception is ipsilateral (on the same side). If it occurs above the level of spinal decussation, the loss occurs on the side contralateral to the site of injury.
