Exteroceptive suppression of the masseter and temporalis muscles and parkinsonian rigidity

Exteroceptive suppression of the masseter and temporalis muscles, produced by electrical stimulation of the mental nerve, was studied in 40 patients with Parkinson's disease (PD) and 18 age-matched control subjects. Prior to the stimulation, background electromyographic activity showed no difference between the normal subjects and patients with PD. The latency in the patients with PD did not differ from that in the normal subjects. The duration and degree of suppression were lower in the patients with PD when compared with the normal subjects. The low level of degree was more obvious in patients with severe rigidity in the neck. A low degree of exteroceptive suppression might play a partial role in causing rigidity.