Slow potentials in the human subthalamus associated with rapid arm movements

During stereotactic operations brain potentials were recorded from the zona incerta of Parkinsonian patients. When the patient performed a rapid contralateral elbow flexion in response to a light signal, a slow positive or positive-negative EEG potential preceded the EMG activation by 30-130 ms (average 60 ms) and extended into the biceps activation phase. It was not evoked by the light flash alone or by rapid passive flexion. The potential may be interpreted as a correlate of movement-related activity of cerebellothalamic pathways mediating command signals for rapid arm movements. In support of this assumption, a marked delay of contralateral biceps activation followed coagulation of the recording site.