The cortex of the human brain contains several turns and convolutions that delimit different brain regions and structures, each with its respective functions and interconnected with each other. One of them is the so-called paracentral lobe, a convolution located in the medial part of the brain 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 belonging to this gyrus perform and what kind of disorders can arise if this region of the brain is damaged.
Paracentral lobe: definition and neuroanatomical location
The paracentral lobe is a convolution of the brain located on the medial surface of the hemisphere, adjacent to the pre-central and post-central convolutions . It includes areas of the frontal lobe and the parietal lobe. It constitutes the most medial part of the upper frontal gyrus.
This brain region is later delimited by the marginal groove; the ascending terminal extension of the cingulate groove, which separates the paracentral lobe from the pre-cuneus. Its lower limit is the cingulate sulcus, which separates this lobe from the cingulate gyrus. In turn, the central groove extends towards the posterior-superior zone of the paracentral lobe, creating the division between the anterior zone of the frontal lobe and the posterior portion of the parietal lobe.
The brain contains numerous convolutions or twists along the entire cerebral cortex, which gives it a wrinkled appearance. It is precisely in the cortex that the higher cognitive functions involving movement planning and management or executive decisions are processed and carried out.
The paracentral lobe can be divided into its anterior and posterior portion : the anterior portion of the paracentral lobe is part of the frontal lobe and is often called the supplementary motor area; and the posterior portion is considered to be part of the parietal lobe, responsible for the somatosensory functions of the distal extremities. Below we will look at the main functions of the areas that are included in this part of the brain.
The paracentral lobe is made up of neural 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, along with the premotor area, is both part of the secondary motor cortex, which is responsible for planning and initiating the movements that will later be executed by the primary motor cortex.
The primary motor cortex , located in the pre-central gyrus and the paracentral lobe, is organized in a somatopic way; this means that the different parts of the body that perform precise movements, such as the hands and the face, are over-represented in a topographic map, compared to other areas, such as the trunk and the legs, that perform thicker 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 in the precentral gyrus, the movements generated will progress from the torso, arm and hand, to the more lateral part of the face.
Disorders related to damage to this brain region
The main clinical manifestations caused by damage to the paracentral lobe areas usually include motor deficits. Patients may show clinical signs such as paresis (feeling of weakness in one or several muscles) or, directly, a plegia or complete muscle paralysis.
Injuries in premotor areas cause alterations in the planning and sequencing of motor actions . Sometimes, a deterioration or an inability to execute learned motor plans is observed, without the existence of muscular paralysis: a disorder called apraxia.
There are several types of apraxia, 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 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 injury or resection of the supplementary motor area, located, as we have mentioned, in the paracentral lobe, is a syndrome that bears his name. The syndrome of the supplementary motor area affects the capacity to initiate movement, initially causing global akinesia. Language impairment and later coordination problems, facial paralysis and hemiplegia may also occur in this region of the brain.
In particular, damage to the left supplementary motor area can lead to transcortical motor aphasia , a disorder that causes a lack of verbal fluency, even though repetition is preserved. There is also a lack of initiative and motivation when it comes to establishing communication, and dysnomy (inability to name objects or people) and a slowing down 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, preventing 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 usually do not present these alterations.
- Cervio, A.; Espeche, M.; Mormandi,R.; Alcorta, S.C. & Salvat, S. (2007). Postoperative supplemental motor area syndrome. Case report. Argentinean magazine 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. Panamerican Medical Ed.