Paracentral Lobe: Characteristics, Location And Functions
The cortex of the human brain contains several gyri and gyri 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 the areas that belong to this gyrus perform and what types of disorders can arise if this region of the brain is damaged.
Paracentral lobe: definition and neuroanatomical location
The paracentral lobe is a gyrus of the brain located on the medial surface of the hemisphere, adjacent to the precentral and postcentral gyri It includes areas of the frontal lobe and the parietal lobe. It constitutes the most medial part of the superior frontal gyrus.
This brain region delimits, posteriorly, the marginal sulcus; the ascending terminal extension of the cingulate sulcus, which separates the paracentral lobe from the precuneus or precuneus. Its lower limit is the cingulate sulcus, which separates this lobe from the cingulate gyrus. For its part, the central sulcus extends toward 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 brain contains numerous convolutions or gyri throughout the entire cerebral cortex, which gives it a wrinkled appearance. The cortex is precisely where higher cognitive functions that involve planning and managing movements or executive decisions are processed and carried out.
The paracentral lobe can be divided into its anterior and posterior portions : The anterior area of ​​the paracentral lobe is part of the frontal lobe and is often called the supplementary motor area; and the posterior portion is considered part of the parietal lobe, responsible for the somatosensory functions of the distal limbs. Next we will see what are the main functions of the areas that are included in this part of the brain.
Features
The paracentral lobe is formed by neuronal nuclei that are responsible for the motor and sensory innervation of the contralateral lower extremities, as well as 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. This area, together with the premotor area, both form part of the secondary motor cortex, responsible for the planning and initiation of movements that the primary motor cortex will later be responsible for executing.
The primary motor cortex , located in the precentral gyrus and the paracentral lobe, are 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, that 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 to a ventrolateral part in the precentral gyrus, the movements generated will progress from the torso, arm and hand, until reaching the most lateral part of the face.
The main clinical manifestations caused by damage to the paracentral lobe areas usually include motor deficits. Patients may present clinical signs such as paresis (a feeling 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 Sometimes, a deterioration 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 with some complexity: for example, brushing one’s 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 injury or resection of the supplementary motor area, located, as we have mentioned, in the paracentral lobe, is a syndrome that bears its name. Supplementary motor area syndrome It affects the ability to initiate movements, initially causing global akinesia. Language alterations and, later, 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 produce transcortical motor aphasia , a disorder that causes verbal disfluency, even though repetition is preserved. There is also a lack of initiative and motivation when establishing communication, and dysnomia (inability to name objects or people) and a slowing of speech may appear, with the appearance of telegraphic language and, sometimes, echolalia (involuntary repetition of words or phrases just heard).
In the most extreme cases, absolute mutism can occur that 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 when executing automated movements are also common, although if patients are able to move voluntarily they do not usually present these alterations.
