Paracentral lobe: characteristics, location, and functions.

What is the paracentral lobe? Let's look at the characteristics of this region of the cortex of the brain.

The cortex of the human brain contains several gyri and convolutions that delimit different brain regions and structures, each of them with their respective functions and interconnected with each other. One of them is the so-called paracentral lobe, a gyrus located in the medial part of the cerebral hemispheres that contains several areas related to the planning and management of motor actions.

In this article we explain what the paracentral lobe is, where it is located, what functions it performs and how it is used.where it is located, what are the functions of the areas belonging to this convolution and what kind of disorders can occur if this region of the brain is damaged.

Paracentral lobe: definition and neuroanatomical localization

The paracentral lobe is a gyrus of the brain located on the medial surface of the hemisphere, contiguous to the precentral and postcentral gyri.. It includes areas of the frontal lobe and parietal lobe. It constitutes the most medial part of the superior frontal gyrus.

This cerebral region delimits, posteriorly, with the marginal sulcus; the ascending terminal extension of the cingulate sulcus, which separates the paracentral lobe from the precentral or precuneus. Its inferior limit is the cingulate sulcus, which separates this lobe from the cingulate gyrus. The central sulcus extends into the posterosuperior area of the paracentral lobe, creating the division between the anterior area of the frontal lobe and the posterior portion of the parietal lobe.

The cerebrum contains numerous convolutions or gyri throughout the cerebral cortex, giving it a wrinkled appearance. It is precisely in the cortex that higher cognitive functions involving the planning and management of movements or executive decisions are processed and carried out.

The paracentral lobe can be divided into its anterior and posterior portionThe anterior area of the paracentral lobe is part of the frontal lobe and is often referred to as the supplementary motor area; and the posterior portion is considered part of the parietal lobe, responsible for the somatosensory functions of the distal extremities. The following are the main functions of the areas included in this part of the brain.

Functions

The paracentral lobe consists of neuronal nuclei responsible for motor and sensory innervation of the contralateral lower extremities, as well as for the regulation of basic physiological functions, such as urination and defecation.

One of the areas included in this lobe is the supplementary motor area, a brain region that is part of the motor cortex and whose main function is to regulate the production of voluntary movements in the musculoskeletal system.The supplementary motor area, a brain region that is part of the motor cortex and whose main function is to regulate the production of voluntary movements in the musculoskeletal system. This area, together with the premotor area, both form part of the secondary motor cortex, responsible for the planning and initiation of movements that will later be executed by the primary motor cortex.

The primary motor cortexThe primary motor cortex, located in the precentral gyrus and the paracentral lobe, is organized somatotopically; this means that the different parts of the body that perform precise movements, such as the hands and face, are overrepresented on a topographic map, compared to other areas, such as the trunk and legs, which perform coarser movements.

For example, when electrodes are used to stimulate the anterior portion of the paracentral lobe, movements of the contralateral leg are initiated. And if these electrodes are then moved from the dorsomedial part to a ventrolateral one in the precentral gyrus, the movements generated will progress from the torso, arm and hand to the most lateral part of the face.

Disorders related to damage in this brain region.

The main clinical manifestations caused by damage to the areas of the paracentral lobe usually include motor deficits. Patients may present with clinical signs such as paresis (sensation of weakness in one or more muscles) or, directly, plegia or complete Muscle paralysis.

Lesions in premotor areas cause alterations in the planning and sequencing of motor actions.. Occasionally, an impairment or inability to execute learned motor plans is observed without muscle paralysis: a disorder called apraxia.

There are several types of apraxias, but the most common motor syndrome when there is damage to premotor areas usually includes the inability to use everyday objects and to produce movements of some complexity: for example, brushing teeth, opening a door or getting dressed. When motor difficulties affect a person's ability to write, the disorder is called agraphia.

Another disorder caused by the lesion or resection of the supplementary motor area, located, as mentioned above, in the paracentral lobe, is a syndrome that bears its name. The supplementary motor area syndrome affects the ability to initiate movements, initially causing a global akinesia. Language impairment and, later on, coordination problems, facial paralysis and hemiplegia contralateral to the damage in this brain region may also appear.

In particular, damage to the left supplementary motor area can lead to transcortical motor aphasia, a disorder that causes lack of fluency in the left supplementary motor area.a disorder that causes lack of verbal fluency, although repetition is preserved. There is also a lack of initiative and motivation in establishing communication, and dysnomia (inability to name objects or people) and a slowing of speech may occur, with the appearance of telegraphic language and, sometimes, echolalia (involuntary repetition of words or phrases just heard).

In the most extreme cases, absolute mutism may occur, preventing the patient from speaking or communicating with others. which prevents the patient from speaking or communicating with others. Motor problems are also relevant, with the appearance of akinesia and loss of movement in the proximal limbs. Difficulties in executing automated movements are also common, although if patients are able to move voluntarily they do not usually present these alterations.

Bibliographic references:

• Cervio, A.; Espeche, M.; Mormandi,R.; Alcorta, S.C. & Salvat, S. (2007). Postoperative supplementary motor area syndrome. Report of a case. Argentine journal of neurosurgery, 21 (3). Autonomous City of Buenos Aires.
• Roland, P. E., Larsen, B., Lassen, N. A., & Skinhoj, E. (1980). Supplementary motor area and other cortical areas in organization of voluntary movements in man. Journal of neurophysiology, 43(1), 118-136.
• Snell, R. S. (2007). Clinical neuroanatomy. Ed. Médica Panamericana.