Supplementary Motor Cortex in Organization of Movement

Traditionally, the SMA has been defined as a single motor area in the medial part of the frontal agranular cortex. Recent anatomical and physiological studies, however, defined two areas in the medial part of Brodmann's area 6. The anterior part is now called the presupplementary motor area (pre-SMA) and the posterior part, the SMA proper or the SMA. Both areas have unique combinations of cortical and thalamocortical connectivity. Although neurons in both areas take some part in simple motor tasks such as pushing buttons in response to sensory signals, characteristic activity is found in the kind of motor tasks that require temporal organization. Temporal sequencing of multiple movements, for instance, requires a role of neuronal activity in both the SMA and pre-SMA.