The cortex of the human brain has many twists and convolutions that give it its peculiar wrinkled appearance. Between these folds we can find the post-central 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 tell you what and where is postcentral rotation, what are the main functions of the somatosensory system that houses and what kinds of disorders occur when damage to this brain structure occurs.
Postcentral rotation: neuroanatomical definition and localization
The postcentral turn is 1 brain convolution 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 to the cerebral cortex) from the sensory input systems.
Nerve projections in the post-central gyrus they include the thalamocortical fibers of the ventral posterolateral and posterolateral nuclei of the thalamus. These nuclei transmit somatosensory signals to both sides of the face and the contralateral body, respectively.
Structurally, the post-central bend is bounded by the medial longitudinal crack (towards the center), by the central groove (in front), by the full post-central groove (behind) and by the lower lateral groove (in low). Although initially defined in the somatosensory cortex as part of Brodmann zones 1, 2 and 3, it is currently considered that this zone should only be considered part of zone 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 often used to describe the distorted human figure, so that it reflects the relative sensory space occupied by each of the body parts in the cerebral cortex.
Certain areas of the body are more sensitive and are overrepresented in the sensory homunculus of the somatosensory cortex, such as the lips, hands, feet, and sex 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.
Postcentral rotation, as we have argued, is a convolution of the brain in which we can locate the primary somatosensory cortex, which is responsible for functions such as location of touch, changes in body temperature, or vibration; voluntary movement of the hands; intentional swallowing; taste perception and language movements, among others.
The primary somatosensory cortex belongs to the somatosensory system, an indispensable part of the sensory nervous system, and the receptor cells function on the basis of thermal stimuli or nociceptive stimuli (related to pain). These can be thermoreceptors, nociceptors, mechanoreceptors or chemoreceptors, depending on the information they transmit.
The association of fibers of the primary somatosensory cortex projects to the white matter of the parietal lobe and connect the post-central gyrus with the somatosensory association zones that integrate tact and conscious proprioception (The sense that allows us to locate and move correctly in space) with other sensory modalities.
Research with phobic subjects has shown that cerebral blood flow increases in the somatosensory cortex (and other areas, such as the frontal cortex, cingulate, insular, and temporal cortex) when participants are presented with a “ object that causes them a specific phobia, with a predominance of sensations before the images in which touch was stimulated.
In contrast, several studies have shown that the upper part of the post-central gyrus is activated in response to blasts of air directed at different parts of the face. This appears to be a region which has the function encode the location of objects close to the face, or those that come in contact with it, And can be used during lactation.
Injuries to the primary somatosensory cortex that houses the postcentral gyrus include characteristic symptoms such as: staesthesia, a sensitive disorder that causes difficulty recognizing numbers, numbers and letters drawn on the skin and palm of the hand; decrease or loss of the sensation of vibration; and reduction or loss of proprioception and fine touch.
Damage to the post-central gyrus usually causes somatosensory alterations in the affected contralateral part, and may also include loss of nociception (emission of pain signals) and thermoception (reception of information about skin and body temperature. ), as well as postural sensitivity.
There are several neurodegenerative disorders and diseases which include altered somatosensory functions by alteration of the post-central gyrus and other related structures. Here are some examples:
1. Corticobasal degeneration
Corticobasal degeneration is a neurodegenerative disease characterized by a progressive and asymmetrical picture of extrapyramidal (stiffness, dystonia, tremors) and cortical (apraxia, cortical sensory alterations, etc.) symptoms.
Patients suffering from this condition show cerebral atrophy involving neuronal nuclei in the precentral and postcentral gyrus, Affecting the primary and secondary somatosensory cortex.
2. Somatosensory crises
Somatosensory seizures or auras are the result of a nerve discharge that affects the post-central gyrus. Contralateral manifestations involving more or less extensive parts of half of the body may include: tingling, numbness, paresthesia or pain sensations.
3. Neglect syndromes
Injuries to the non-dominant parietal lobe (usually the right one) can cause heminegligence, in which the opposite side of the environment is ignored even though vision is normal.
Some patients with these disorders may develop associated neurological impairments, such as limb paralysis, Although they are generally unaware of their deficits and may deny them (anosognosia).
4. Proprioceptive deficits
Damage to postcentral rotation of the parietal lobe, dorsal columns, or dorsal root ganglia can result in loss of proprioception, asterognosia (inability to identify objects by touch), loss of vibrational sensations, and loss of discrimination in two points in the trunk or limbs.
When the lesion passes 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 cord decussation, loss occurs on the contralateral side of the injury site.
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- Pain perception: is there a role in the primary somatosensory cortex ?. Proceedings of the National Academy of Sciences, 96 (14), pages 7705-7709.
- Snell, RS (2007). Clinical neuroanatomy. Pan American Medical Ed.