The cortex of the human brain contains several twists 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 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 found, what functions evolve the areas belonging to this convolution 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 1 brain convolution located on the medial surface of the hemisphere, contiguous to the precentral and postcentral convolutions. It includes areas of the frontal lobe and parietal lobe. It forms the most medial part of the superior frontal gyrus.
This cerebral region is delimited later with the marginal groove; the ascending terminal extension of the cingulate groove, which separates the paracentral lobe from the precuña or precúneo. Its lower limit is the cingulate groove, which separates this lobe from the cingulate gyrus. For its part, the central groove extends to the postero-superior zone of the paracentral lobe, creating the division between the anterior zone of the frontal lobe and the posterior part of the parietal lobe.
The brain contains numerous convolutions or twists along the entire cerebral cortex, giving it a wrinkled appearance. In the cortex, this is precisely where higher cognitive functions involving the planning and management of movements or executive decisions are processed and executed.
The paracentral lobe can be divided into its anterior and posterior part: The anterior area of the paracentral lobe is part of the frontal lobe and is often referred to as the supplementary motor zone; and the posterior part 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 included in this part of the brain.
The paracentral lobe is made up of neural nuclei responsible for motor and sensory innervation of the contralateral lower limbs, 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 additional motor area, A region of the brain 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 zone, forms the two parts of the secondary motor cortex, responsible for planning and initiating movements that will later be responsible for the execution of the primary motor cortex.
The primary motor cortex, Located in the precentral gyrus and paracentral lobe, are somatotopically organized; this means that the different parts of the body that perform precise movements, such as the hands and face, are over-represented on a topographic map, compared to other areas, such as the trunk and legs, which make thicker movements.
For example, when electrodes are used to stimulate the anterior part of the paracentral lobe, contralateral movements of the legs are initiated. And if then these electrodes pass from the dorsomedial part to a ventrolateral part in the precentral convolution, the generated movements will progress of the torso, the arm and the hand, until arriving at the most lateral part of the face.
Disorders related to damage in this area of the brain
The main clinical manifestations caused by lesions of 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, pleurisy or complete muscle paralysis.
Injuries in the premotor areas lead to alterations in the planning and sequence of motor actions. Sometimes there is deterioration 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 the premotor areas usually includes the inability to use everyday objects and produce movements with some complexity: for example , brush your teeth, open a door or get dressed. When motor difficulties affect a person’s ability to write, the disorder is called stapling.
Another of the disorders caused by the injury or resection of the additional motor zone, located, as we have mentioned, in the paracentral lobe, is a syndrome that bears its name. Supplementary motor zone syndrome affects the ability to initiate movement, initially causing overall akinesia. Language changes and later coordination problems, facial paralysis and hemiplegia contralateral to lesions in this brain region may also appear.
In particular, damage to the left supplementary motor area can lead to transcortical motor aphasia, A disorder which causes a lack of verbal fluency, although repetition is preserved. There is also a lack of initiative and motivation when establishing communication, and dysnomy (inability to name objects or people) and slowing of speech may appear, with the advent of telegraph language. and sometimes, echolalia (involuntary repetition of recently heard words or phrases). ).
In the most extreme cases, absolute dumbness can occur which prevents the patient from speaking or communicating with others. Motor problems are also relevant, with the onset of akinesia and loss of movement in the proximal limbs. Difficulties in performing automated movements are also common, although if patients are able to move voluntarily, they usually do not exhibit these alterations.
- Cervio, A .; Espeche, M .; Mormandi, R .; Alcorta, SC and Salvat, S. (2007). Postoperative supplementary motor zone syndrome. Report a case. Argentine Journal of Neurosurgery, 21 (3). Autonomous City of Buenos Aires.
- Roland, PE, Larsen, B., Lassen, NA and Skinhoj, E. (1980). Complementary motor area and other cortical areas in the organization of voluntary movements in humans. Journal of Neurophysiology, 43 (1), 118-136.
- Snell, RS (2007). Clinical neuroanatomy. Pan American Medical Ed.