Cortical activation during fast repetitive finger movements in humans: dipole sources of steady-state movement-related cortical potentials.

Fast repetitive finger movements are associated with characteristic EEG patterns described in humans as steady-state movement-related cortical potentials (ssMRCPs). The objective of the present study was to determine the electrical generators of ssMRCPs (movement rate, 2 Hz) by dipole modelling. The generators for the initial ssMRCP phase (peak approximately 60 msec before EMG onset) were located in the central region bilaterally, with largely radial orientation, consistent with activation of the crown of the precentral gyrus. The generator of the next phase (peak approximately 10 msec after EMG onset) was located in the contralateral central region with tangential posterior orientation, consistent with activation of the anterior wall of the central sulcus. The postmovement phase (peak approximately 95 msec after EMG onset) was explained by another source in the contralateral central region with tangential anterior orientation, consistent with activation of the posterior wall of the central sulcus. This pattern probably corresponds to a sequence of activation of the bilateral dorsal premotor cortex, contralateral primary motor, and primary somatosensory cortex that takes place within approximately 200 msec around EMG onset. Steady-state movement-related cortical potentials in combination with dipole modelling provide a novel, noninvasive approach to assessing changes of human cortical premotor, motor, and somatosensory activation in the millisecond range.