Subregions within the supplementary motor area activated at different stages of movement preparation and execution

Previous studies have provided evidence that the primary motor area (M1) is involved in actual execution of a motor program, while the premotor area (PreMA) and the supplementary motor area (SMA) play a role in its preparation. We have used the high temporospatial resolution of functional magnetic resonance imaging (fMRI) to study the relationship between stages of a motor program and activation of these motor-related cortical areas. Seven normal volunteers performed a delayed-motor task in which the preparation of finger movements was dissociated in time from movement execution, while event-related fMRI was obtained. The M1 and PreMA showed expected activation associated with execution and preparation stages, respectively. Within SMA, subregions with different temporal profiles of activation were identified: The anterior part became activated early in the preparation period, whereas the posterior part only with movement execution. This supports the notion that the classic SMA consists of the pre-SMA and SMA proper each with different functions.