Sequential activation of supplementary motor area and primary motor cortex during self-paced finger movement in human evaluated by functional MRI.

The 'Bereitschaftspotential' attributed to activation of the supplementary motor area (SMA) precedes the 'motor potential' of the primary motor cortex (Ml) about 500-1000 ms during self-initiated movements. A measurement procedure is reported to evaluate the sequence of hemodynamic activation within both motor areas by functional magnetic resonance imaging (fMRI). The fMRI-data were averaged across multiple trials of single voluntary finger movements and analyzed with respect to the onset-time of signal increase. All participants showed a sequential hemodynamic response with SMA preceding M1 activation. The mean latency between hemodynamic activation of SMA and M1 amounted to 0.8 s. These findings suggest that the vascular response parallels the electrical events and that a sufficient temporal resolution can be achieved by fMRI to detect sequential hemodynamic activation of functionally connected cortical areas.