Supplementary Motor Area: What It Is, Function And Injury

He supplementary motor area (SMA) It is a part of the cerebral cortex, it is a premotor area whose main function is motor planning or programming and bimanual coordination.

In 1951, Penfield and Welch coined this term. However, there is still a lot to discover exactly some of its functions. In recent years, progress has been made thanks to new imaging and neurophysiology techniques, including positron emission tomography (PET) and functional magnetic resonance imaging (fMRI).

Cortical areas involved in motor control and their main functions

When we talk about motor control, the first thing that should be kept in mind is that the organization of the cortex does not only involve areas that are exclusively motor.

• First of all, there are association areas where we find the posterior parietal cortex and the dorsolateral prefrontal cortex. These provide sensory and motivational cues for target-directed movements and select the most appropriate strategy to execute a movement.
• On the other hand, there are motor areas where are the premotor areas or secondary motor cortex (Broadmann area 6). This is where we find the premotor cortex (lateral area) and the supplementary motor area (upper and medial area). These are responsible for motor planning, specifically the premotor cortex for movements triggered by external stimuli and the AMS for bimanual coordination.
• There is also the primary motor area (Broadmann area 4), which is responsible for initiating or triggering movement. Specifically, it has the function of developing the motor commands for when and how the muscles are to move.

What part of the brain controls the motor part? In the following article you will find more information about The cerebral cortex: functions and parts.

If you are wondering where this area is, you should know that the supplementary motor area is located in the medial aspect of the frontal lobein the agranular cortex of Broadmann number 6 It extends posteriorly to the primary motor cortex and inferiorly to the cingulum. That is, it is the region of the association motor cortex of the dorsal and dorsomedial areas of the frontal lobe, rostral to the primary motor cortex.

What function does the motor area fulfill? The supplementary motor area is essential for our control of movement. His injury would produce great deficits in our daily lives. Below are some of its functions. Let’s see which ones there are:

1. Planning or motor programming and bimanual coordination.
2. It is involved in the motor learning. Specifically in the ability to learn response sequences in which the execution of one response constitutes the signal that the next response is to be given.
3. Participation in different stages of the movement initiationsequence and control of this.
4. Involvement in the reception of sensory stimuli.
5. Participation in the work memory.
6. Recovery and repetition of previously learned tasks.
7. Participation in language tasks, in the control of articulation and phonation. In this article we talk about the main areas of language: Broca and Wernicke’s area.
8. It acts as a connection between the limbic system and executive motor apparatusso it acts by translating the motive from intention to action and exerting control over the primary motor cortex.

What can affectation of the supplementary motor area mean? Several authors, including Pendfield, have reported cases of Transient speech motor deficits after supplementary motor area (SMA) resection However, it has not been possible to correlate clinical findings with anatomy. One of the pioneers was Laplane (1977), who described the clinical evolution of postsurgical deficit after resections limited to the medial part of the posterosuperior region of the frontal lobe in 3 patients.

Surgery in or near the supplementary motor area can produce a set of characteristic deficit symptoms that are included in the so-called AMS syndrome. 3 stages occur:

1. Immediately after surgery: global askinesia (greater on the contralateral side) and language arrest
2. A few days after surgery: severe reduction of contralateral spontaneous motor activity, emotional facial paralysis and reduction of spontaneous speech.
3. Time after surgery: difficulty performing alternating movements with the hands. This spectrum of severe but transient deficit following involvement of the ipsilateral SMA has been termed “MA syndrome.”

Some studies suggest that recovery of movement is usually complete after 11 days. Fine movements may take 2 to 6 weeks to recover. Instead, Bimanual or complex tasks that require them can remain a permanent deficit.

Finally, add that, as has been mentioned throughout this article, this area is usually related to language and therefore it is important to mention that language deficit syndrome can appear in SMA lesions in the dominant hemisphere and is extremely characterized by mutism However, this defect usually recovers little by little, giving way to transcortical motor dysphasia with severe predominantly motor dysphasia and telegraphic speech. There are also studies that comment on the presence of deficits such as verbal learning and alterations in the understanding and expression of language

This article is merely informative, at PsychologyFor we do not have the power to make a diagnosis or recommend a treatment. We invite you to go to a psychologist to treat your particular case.

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