Supplementary motor area

The supplementary motor area (SMA) is a part of the sensorimotor cerebral cortex (perirolandic, i.e. on each side of the Rolando or central sulcus). It was included, on purely cytoarchitectonic arguments, in area 6 of Brodmann and the Vogts. It is located on the medial face of the hemisphere, just in front of the primary motor cortex. This is an element that appeared late in evolution, in monkeys, linked to the appearance of a true medial pallidum.

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Structure

Recently, it was found that the SMA is likely made up of two functionally distinct parts, and was divided into the SMA proper and the pre-SMA. Additionally, the SMA proper is also subdivided into the caudal SMA and the rostral SMA. In primates, the SMA proper is analogous to area F3, whereas the pre-SMA is analogous to area F6.

In monkeys it is a part of the dysgranular cortex. This means an intermediate differentiation between the more posterior agranular motor cortex and the more anterior granular eulaminate frontal cortex. In monkeys after the discovery of this area a "preSMA" was found. It is thus important to check in literature if preSMA was in fact included or not.

Function

The SMA is implicated in the planning of motor actions. One could say that the SMA sends a "plan" of the motor action to the primary motor cortex, which executes the action. In contrast to the premotor cortex (PMC) the SMA is involved in actions that are under internal control, such as actions based on memory (as opposed to actions based on a visual cue).

References

Principles of Neural Science (2000), 4th ed., Kandel et al.

Debaere,-F; Wenderoth,-N; Sunaert,-S; Van-Hecke,-P; Swinnen,-S-P (2003). Internal vs external generation of movements: differential neural pathways involved in bimanual coordination performed in the presence or absence of augmented visual feedback. Neuroimage. 2003 Jul; 19(3): 764-76

Vorobiev et al. (1998) Parcellation of human mesial area 6: cytoarchitectonic evidence for three separate areas. Eur J Neurosci. 10(6):2199-203.