Voluntary responses to peripheral stimulation in Parkinson's disease. An electrophysiological study

Voluntary motor responses of 15 patients with Parkinson's disease and 5 normal subjects in the same age group were examined electromyographically. The reaction time (RT) (period of latency) and the successive reaction (SR) time (between two quick repetitive voluntary movements) of the facial, eye and masseter muscles following electrical stimulation from the periphery (thenar muscles) were measured. In the patients the RT and SR time following peripheral stimulation were obviously delayed. These results suggest that cortical motor areas are involved in Parkinson's disease so that, following peripheral stimulation, cortical activity is inhibited for a relatively long time. This occurs most often following two brisk repetitive voluntary muscle movements (SR).