Relationship between motor activity-related cortical potential and voluntary muscle activation

The purpose of this study was to investigate the relationship between EEG-d erived motor activity-related cortical potential (MRCP) and voluntary muscl e activation. Eight healthy volunteers participated in two experimental ses sions. In one session, subjects performed isometric elbow-flexion contracti ons at four intensity levels [10%, 35%, 60%, and 85% maximal voluntary cont raction (MVC)]. In another session, a given elbow-flexion force (35% MVC) w as generated at three different rates (slow, intermediate, and fast). Thirt y to 40 contractions were performed at each force level or rate. EEG signal s were recorded from the scalp overlying the supplementary motor area (SMA) and contralateral sensorimotor cortex, and EMG signals were recorded from the skin surface overlying the belly of the biceps brachii and brachioradia lis muscles during all contractions. In each trial, the force was used as t he triggering signal for MRCP averaging. MRCP amplitude was measured from t he beginning to the peak of the negative slope. The magnitude of MRCP from both EEG recording locations (sensorimotor cortex and SMA) was highly corre lated with elbow-flexion force, rate of rising of force, and muscle EMG sig nals. These results suggest that MRCP represents cortical motor commands th at scale the level of muscle activation.