Supplementary motor area (brain): parts and functions
Moving is fundamental to our survival. However, every action we take is not done by magic: it requires a series of complex preparation and planning processes and finally the initiation of the sequence of movements required for such action.
At the brain level we find that the motor cortex is the main brain region (although not the only one) responsible for this control. And between the different areas that configure it and help the beginning and realization of the movement we can find the supplementary motor area , one of the most important parts of the brain when it comes to 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 , this being 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 band at the top and medial 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 the Rolando fissure. It corresponds to area 6 of Brodman.
The supplementary motor area is together with the premotor area part of the secondary motor cortex , that allows to plan, program and initiate the control of the movements that the primary motor area will subsequently carry out.
As regards specifically the supplementary motor area, although part of its functions and importance are not completely known, it has been seen to have a relevant implication at the time of starting the 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. It is important not only in the initiation of the movement but also in its preparation and monitoring . For example, a relationship between this area and motor coordination has been seen 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.
Preliminary motor area
This part of the supplementary motor area it is characterized by activating 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
Own supplementary motor area
In this region, 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 orders to move without needing to react to any stimulation for it.
The supplementary motor area is important in the planning and coordination of movement, as well as the motivation to start it 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 time there is a recovery), some of which are attributed are the following.
1. Motivation and beginning of the movement
One of the functions most linked to the supplementary motor area is to generate the necessary motivation to carry out and initiate the movement. It has been seen in situations in which this region was injured, akinesia appeared or lack of voluntary movement.
2. Start of speech
In the previous point we mentioned that the supplementary motor area affects the initiative to move. Within the various possible movements they also include those of the language , with what is fundamental to allow establishing communication between the subject and other people.
3. Coordination of precise movements
The realization of 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 before this type of acts.
4. Preparation for movement
The supplementary motor area is also linked to the preparation for movement, activating when someone imagines the realization of complex movements even if 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 the movement as a reaction to environmental stimulation . With this we are not referring to reflections but to the realization of voluntary movements in concrete situations.
Alterations generated by your injury
Surgical area syndrome has been identified from surgical resection or injury to the area. It has been observed that resection of the supplementary motor area generates initial global akinesia and language alteration, after which there is incoordination, facial paralysis and hemiplegia contralateral to the lesion. Also problems of motor control, although the functionality can be recovered in a period that can reach up to six months. However, sometimes some problems remain in the fine movement, especially of the hands .
The injury 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, the absence of initiative and motivation to establish communication is generated, with frequent occurrence of dysnomia (difficulty in 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, they are reduced to a minimum in what is known as akinesia, although the loss of willingness to move in the proximal parts of the body predominates. It is common for problems to appear in the realization of automated movements, although if the patient moves voluntarily there are usually no alterations.
- You may be interested: "The 6 types of aphasia (causes, symptoms and characteristics)"
- Cervio, A .; Espeche, M .; Mormandi, R .; Alcorta, S.C. & Salvat, S. (2007). Syndrome of the postoperative supplementary motor area. Report of a case. Argentine neurosurgery journal, 21 (3). Autonomous City of Buenos Aires.
- Herrera, R.F. (2012). Clinical syndrome due to removal of the supplementary motor area in patients with cerebral gliomas. Doctoral thesis. Open University Interamericana. 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.