SEVERAL hypotheses have been proposed for the mechanism of abnormal movements, with the greatest emphasis placed upon the role of central structures. 1-3 While the importance of muscle afferents has also been stressed, 4 little attention has been paid to other peripheral receptors. However, observations made during a series of stereotactic thalamotomies suggest that impulses transmitted over the specific somatosensory pathways are also concerned in dyskinesia. Materials and Methods Cortical and subcortical potentials evoked by transcutaneous electrical stimulation of the median nerve were recorded during 42 stereotactic thalamotomies in patients with dyskinesia. The cortical responses were detected by pin electrodes placed in the scalp, and the depth responses by concentric, bipolar, Teflon insulated, stainless steel electrodes with an outer diameter of 1.4 mm and tip separation of 0.5 mm. An averaging computer was used to retrieve the evoked potentials. 5 The electrodes were directed toward nucleus ventralis posterior lateralis