Response properties of the perioral reflex in Parkinson's disease.

Analyses of the response magnitudes of the short-latency perioral reflex were made in a group of Parkinson disease patients and control subjects. As a group, the parkinsonian subjects manifested reflex magnitudes which were increased relative to normal. For low-acceleration, mechanical displacements of perioral tissue (less than 500 cm/s2), the perioral reflex was not elicited in normal controls. However, such low-acceleration stimuli did elicit the perioral reflex in more than half of the parkinsonian subjects studied. These findings are consistent with earlier findings of increased sensitivity of facial and perioral reflexes associated with disturbances of the basal ganglia. These results contribute to the understanding of specific stimulus-response characteristics of the facial reflex and the role of the basal ganglia in orofacial motor control. The finding of increased sensitivity to mechanical stimuli in Parkinson's disease supports the hypothesis of basal ganglia gating or regulation of afferent information.