Supplementary motor area (brain): parts and functions

Moving is essential for our survival. However, each action we carry out is not carried out by magic: it requires a series of complex preparation and planning processes and finally the initiation of the sequence of movements required for said action.

At the brain level, we find that the motor cortex is the main brain region (although not the only one) in charge of said control. And among the different areas that configure it and help to start and carry out the movement we can find the supplementary motor area, one of the most important parts of the brain when interacting with the environment.

• Related article: "Parts of the human brain (and functions)"

The supplementary motor area: a part of the motor cortex

The supplementary motor area is a brain region that is part of the motor cortex, being this one of the main areas of the brain that allow the realization of voluntary movements in the musculoskeletal system.

This area can be found in a strip in the upper and medial part of both hemispheres, in the frontal lobe. Specifically, it is located in front of the primary motor cortex, which in turn is located immediately anterior to Rolando's fissure. It corresponds to area 6 of Brodman.

The supplementary motor area It is, together with the premotor area, part of the secondary motor cortex., which allows planning, scheduling and initiating the control of the movements that the primary motor area will subsequently carry out.

With regard specifically to the supplementary motor area, although part of its functions and importance are not fully known, it has been given that it has a relevant implication when starting the movement and the motivation and activation necessary to produce a motion.

His connection with limbic system and the basal ganglia generates that there is a relationship between movement and motivation. Likewise, its activity it is important not only in the initiation of the movement but also in its preparation and monitoring. For example, a relationship has been seen between this area and motor coordination in situations that require precise and complex control.

• Related article: "Motor cortex of the brain: parts, location and functions"

Divisions of this part of the brain

The investigations carried out differentiate at least two parts in the supplementary motor area.

presupplementary motor area

This part of the supplementary motor area It is characterized by being activated and generating movement linked to external stimulation. In other words, it is the part that generates the beginning of the movement as a reaction to the environment.

own supplementary motor area

In this region, neuronal activity does not depend on stimulation but rather on the voluntary realization of one's own movement. It is the one that initiates the sequence of orders to move without the need to react to any stimulation for it.

functions

The supplementary motor area is important in the planning and coordination of movement, as well as the motivation to start and carry it out. Although its real importance and some of its functions are not completely known (for example, its resection alters different functions but nevertheless in many cases after a while a recovery occurs), some of which are attributed to it are the following.

1. Motivation and initiation of movement

One of the functions most linked to the supplementary motor area is to generate the necessary motivation to carry out and start the movement. it has been seen in situations in which this region was injured, appearing akinesia or lack of voluntary movement.

2. onset of speech

In the previous point we have mentioned that the supplementary motor area affects the initiative to move. Among the various possible movements those of the language are also included, which is essential to allow establishing communication between the subject and other people.

3. Coordination of precise movements

Carrying out complex motor sequences that require great precision, such as those that require the use of both hands, depends on different brain areas. One of them is the supplementary motor area, which shows activation in the face of this type of act.

4. preparation for movement

The supplementary motor area is also linked to movement preparation, being activated when someone imagines performing complex movements. although I do not carry them out.

5. reaction to stimuli

As we have indicated, one of the parts of the supplementary motor area is linked to the initiation and planning of movement as a reaction to environmental stimulation. With this we are not referring to reflexes but to the performance of voluntary movements in specific situations.

Alterations generated by your injury

From surgical resection or injury to the area, a supplementary motor area syndrome has been identified. Resection of the supplementary motor area has been observed to generate initial global akinesia and altered language, followed by incoordination, facial paralysis, and hemiplegia contralateral to the injury. Also motor control problems, although functionality can be recovered in a period that can reach up to six months. However, on occasion some fine movement problems remain, especially of the hands.

Lesion in the left supplementary motor area often leads to transcortical motor aphasia., in which language production is not fluent despite maintaining the ability to repeat another person's words. In general, the lack of initiative and motivation to establish communication is generated, being frequent appear dysnomia (difficulty naming) and slowing down, with telegraphic language and sometimes echolalia. Nor is it strange that mutism occurs and the subject does not speak or communicate.

Also at the level of movement, these are reduced to a minimum in what is known as akinesia, although the loss of will to move predominates in the proximal parts of the organism. It is common for problems to appear when performing automated movements, although if the patient moves voluntarily, there are usually no changes.

• You may be interested in: "The 6 types of aphasia (causes, symptoms and characteristics)"

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.
• Herrera, R.F. (2012). Clinical syndrome due to removal of the supplementary motor area in patients with brain gliomas. PhD thesis. Interamerican Open University. Rosario Regional Headquarters. Faculty of Medicine and Health Sciences.
• Monterroso, M.E.; Avilez, A.B. and Vanegas, M.A.A. (2008). Supplementary motor area. Arch. Neurocien, 13 (2): 118-124. Mexico.