It is commonly understood that the primary motor strip, or M1, is where cell bodies of neurons are found in a organised manner, forming the first part of the path innervating striated muscle. But how are impulses through this area orchestrated to create the possible motor actions of our bodies?
Before the 21st century the supplementary motor area (SMA) was recognised as involved in motor activity because of increased blood flow. It lies just anterior to M1.
Another area, called the pre-SMA, is found more anterior and medially; on the superior frontal gyrus.
Compared to the primary motor cortex, the SMA's blood flow was greater during complex motor tasks, and even during visualisation of actions.
Pacing tasks on external stimuli (metronome, visual cues) or internal stimuli correlates with whether the SMA or pre-SMA are active.
Pre-SMA is correlated with novel tasks, or early during skill acquisition, whereas the SMA proper is with established, complex tasks (like playing scales).
It appears that the SMA may, crudely speaking, be necessary for coordinating simple or learned movements. In contrast the pre-SMA is probably necessary to train new movements.
This has clinical relevance for focal brain injury to the motor areas when considering how much function may be recovered with rehabilitation.
Motor areas of the medial wall: a review of their location and functional activation.
Picard N, Strick PL.
Cereb Cortex. 1996
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