Abstract
The motor cortex outputs neural commands to recruit motor units (MUs) according to the intended movement. Only a few previous studies have succeeded in recording the cortical potentials related to the MU recruitment (Kato and Tanji, 1972; Kristeva and Kornhuber, 1980). However, because these studies examined a cortical potential related to only the MU having the lowest recruitment threshold force (RTF) values recruited at the movement onset, it seems likely that these potentials included not only the cortical activity for MU recruitment, but also that for intended movement. Therefore, we attempt to record the cortical potentials involved in the recruitment motor units during gradual force exertion isolating movement onset. Subjects were asked to exert isometric contraction increasing the force gradually and slowly (Ramp contraction) by their index finger. More than two MUs had different RTF values were recorded from the first dorsal interosseous muscle concurrently. The EEG was averaged with respect to the first spike of discharges in each MUs. We observed the two cortical potentials. First, we observed negative slope before the movement, but it seemed to be the readiness potential rather than the activity for MU recruitment. Second, sharp negative deflection appeared after the first spike of several MU discharges.We confirmed cortical potentials related to recruiting single MUs under recruitment progressing isolating movement onset. [J Physiol Sci. 2007;57 Suppl:S160]
