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 various gyri 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 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 type of disorders can arise if this region of the brain is damaged.
Paracentral lobe: definition and neuroanatomic location
The paracentral lobe is a gyrus of the brain located on the medial surface of the hemisphere, contiguous with the precentral and postcentral gyri. Includes areas of the frontal lobe and the parietal lobe. It is the most medial part of the superior frontal gyrus.
This cerebral region delimits, later, with the marginal sulcus; the ascending terminal extension of the cingulate sulcus, which separates the paracentral lobe from the pre-wedge or precuneus. Its lower limit is the cingulate sulcus, which separates this lobe from the cingulate gyrus. For its part, the central sulcus 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 gyri throughout the cerebral cortex, giving it a wrinkled appearance. In the cortex it is precisely where the 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 paracentral lobe is part of the frontal lobe and is often called the supplementary motor area; and the posterior portion is considered as part of the parietal lobe, responsible for the somatosensory functions of the distal extremities. Next we will see what are the main functions of the areas that are included in this part of the brain.
The paracentral lobe is made up of neuronal nuclei that are 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. This area, together with the premotor area, are both part of the secondary motor cortex, responsible for the planning and initiation of movements that, later, will be responsible for executing the primary motor cortex.
The primary motor cortex, located in the precentral gyrus and the paracentral lobe, is somatotopically organized; This means that 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 more gross movements.
For example, when electrodes are used to stimulate the anterior 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 they reach the most 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 present with clinical signs such as paresis (a feeling of weakness in one or more muscles) or, directly, a plegia or complete muscle paralysis.
Lesions in premotor areas cause alterations in the planning and sequencing of motor actions. Sometimes there is an impairment or an inability to execute learned motor plans, without muscle 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 dressing. When motor difficulties affect a person’s ability to write, the disorder is called agrafia.
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 his name. The supplementary motor area syndrome 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 lead to transcortical motor aphasia, a disorder that causes a lack of verbal fluency, although repetition is preserved. There is also a lack of initiative and motivation when establishing communication, with the possibility of dysnomia (inability to name objects or people) and slowing of speech, with the appearance of telegraphic language and, on occasions, echolalia (involuntary repetition of words or phrases just heard).
In the most extreme cases, a complete silence 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 in executing automated movements are also common, although if patients are able to move voluntarily they do not usually present these alterations.
- Cervio, A .; Espeche, M .; Mormandi, R .; Alcorta, SC & Salvat, S. (2007). Postoperative supplementary motor area syndrome. Report of a case. Argentine journal of neurosurgery, 21 (3). Autonomous City of Buenos Aires.
- Roland, PE, Larsen, B., Lassen, NA, & 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, RS (2007). Clinical neuroanatomy. Panamerican Medical Ed.