Moving is fundamental to our survival. However, every action we take is not done by magic: it requires a series of complex processes of preparation and planning and finally the initiation of the sequence of movements required for that action.

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

The supplementary motor area: a part of the motor cortex

The supplementary motor area is a brain region that forms part of the motor cortex , which is one of the main areas of the brain that allows voluntary movements in the musculoskeletal system.

This area can be found in a strip at the top and middle of both hemispheres, in the frontal lobe. Specifically, it is located in front of the primary motor cortex, which in turn is located immediately before Rolando’s cleft. It corresponds to Brodman’s area 6.

The supplementary motor area is together with the premotor area part of the secondary motor cortex , which allows planning, programming and starting the control of the movements that will be carried out later by the primary motor area.

With specific regard to the supplementary motor area, although some of its functions and importance are not completely known, it has been seen to have a relevant involvement in initiating movement and the motivation and activation necessary to produce a movement.

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

Divisions of this part of the brain

The research carried out differentiates at least two parts in the supplementary motor area.

Budgetary motor area

This part of the supplementary motor area is characterised by activation and generation of 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 the neuronal activity does not depend on stimulation but rather on the voluntary realization of the movement itself . It is the one that initiates the sequence of commands to move without the need to react to any stimulation to do so.

Functions

The supplementary motor area is important in the planning and coordination of the movement, as well as in the motivation to initiate 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 some time there is a recovery), some of the functions attributed to it are the following.

1. Motivation and initiation of movement

One of the functions most linked to the supplementary motor area is that of generating the necessary motivation to perform and initiate the movement. This has been seen in situations where this region was injured, with akinesia or lack of voluntary movement appearing.

2. Beginning of speech

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

3. Coordination of precise movements

The performance of complex motor sequences that require great precision , such as those requiring the use of both hands, depends on different brain areas. One of them is the supplementary motor area, which shows activation before this type of acts.

4. Preparation for movement

The supplementary motor area is also linked to the preparation for movement, being activated when someone imagines performing complex movements even if they 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 movement initiation and planning as a reaction to environmental stimulation . By this we are not referring to reflexes but to the performance of voluntary movements in concrete situations.

Alterations generated by your injury

A supplemental motor area syndrome has been identified from surgical resection or injury to the area. It has been observed that the resection of the supplementary motor area generates initial global akinesia and alteration of language, after which uncoordination, facial paralysis and hemiplegia appear against the lesion. Also motor control problems, although functionality can be recovered in a period that can reach up to six months. However, sometimes some problems remain in fine movement, especially of the hands .

The lesion in the left supplementary motor area usually generates transcortical motor aphasia , in which the production of language is not very fluid despite maintaining the ability to repeat the words of another person. In general, there is a lack of initiative and motivation to establish communication, and dysnomy (difficulty in naming) and slowing down are frequent, with telegraphic language and sometimes echolalia. It is also not strange that mutism appears 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 in the proximal parts of the body predominates. It is common for problems to appear in the performance of automated movements, although if the patient moves voluntarily there are usually no alterations.

Bibliographic references:

  • 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.
  • Herrera, R.F. (2012). Clinical syndrome by removal of the supplementary motor area in patients with brain gliomas. Doctoral 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.