Cortical and spinal motor excitability during the premovement EMG silent period prior to rapid voluntary movement in humans

(1) To delineate the cortical and spinal excitability during the pro-movement silent period (PMSP), the motor-evoked potentials (MEPs) and H-reflexes were measured for 0-150 ms prior to rapid voluntary movements of I I healthy subjects. The appearance of PMSP was judged from the electromyogram of the agonist muscle at each rapid movement and the differences of MEPs or H-reflex between the movement which PMSP appeared (PMSP MEPs or PMSP H-reflex) and the movement which did not appear (non-PMSP MEPs or non-PMSP H-reflex) were compared. (2) The mean amplitudes of the PMSP MEPs in die flexor carpi radialis were significantly smaller than the non-PMSP MEPs, whereas the mean amplitude of the PMSP H-reflex was not significantly different from the non-PMSP H-reflex. (3) In the soleus muscle, the change in MEPs and H-reflexes was examined at three periods for 0-150 ins before the rapid movements. The mean amplitudes of PMSP MEPs for the - 150- to - 100-ms period and for the -50- to -5-ms period were significantly smaller than those of non-PMSP MEPs. On the other hand, the differences of the mean amplitudes between PMSP H-reflex and non-PMSP H-reflex at the three periods were not significant. (4) These findings suggested that the cortical sensitivity to the TMS was decreased during PMSP though the spinal inhibitory mechanisms assess by H-reflex was not altered during the PMSP and that the EMG pause of the PMSP originates not at the spinal level but at the cortical level. The data support the hypothesis that PMSP is preprogrammed in the preparation and initiation process of the voluntary movements aimed at reinforcement of the performance of the subsequent ballistic movements. (C) 2002 Elsevier Science B.V. All rights reserved.