Cerebral motor potential preceding grip strength movement.

The relationship between the force of the movement and the motor potential (MP), and that between the degree of the muscular discharge and the MP were examined by the method of bipolar and monopolar derivation. The MP amplitudes were significantly higher at C3' and Cz than at other lead placements for right grip and higher at C4' and Cz for left grip. A significant difference was observed among all lead placements except at Cz-C4'. The MP amplitudes were significantly higher for a strong grip task than for a weak grip tasks. Moreover, the MP amplitudes were higher at higher degrees of muscular discharge. The MP usually occurred about 100 msec prior to the EMG discharge, as also confirmed by Deecke et al. Therefore, from the present results and other studies, we postulated that the MP may reflect the activity of the neurons in the motor and premotor cortices, which might contribute to movement initiation. In addition, the MP amplitudes measured using bipolar derivation were more explicit than those measured using monopolar derivation.