Reduced late component of exteroceptive reflex in patients with Parkinson's disease.

The exteroceptive reflexes in the masseter muscles in patients with Parkinson's disease (PD) were examined. The reflex produced by 3 Hz mental nerve stimulation consisted of four negative peaks and three positive peaks in the unrectified recordings. The latencies of the peaks in patients with PD were the same as those in control subjects, except for the P2 component in the right masseter muscle. The amplitudes of N3-P3 and P3-N4 were smaller in patients with PD than those in control subjects. Interpeak latency of N3-N4 was shorter in PD patients. Exteroceptive suppression in the masseter muscles was also examined. The early component (ES1) of so-called exteroceptive suppression was normal in patients with PD. The duration and degree of the late component (ES2) of exteroceptive suppression decreased in patients with PD. According to the latencies, N1 and N2 speaks seem to be the onset and end of ESI; N3 and N3 peaks the onset and end of ES2, respectively. The early component did not show any significant abnormality. Reduced late component of exteroceptive reflex in patients with PD might be related to the abnormal motor control system of the facial muscles.