PHYSIOLOGICAL TREMOR IN HUMAN JAW-MUSCLE SYSTEM

Small, quasi-rhythmical tremor of the jaw occurs at rest and during vo luntary movements. In peripheral limbs, tremor consists of a component due to mechanical resonance properties of the system, and a neurogeni c component mediated by a central pacemaker or neural loops. The prese nt study attempted to determine if these components were present in ja w tremor measured with a position transducer held lightly between the incisors. When weights were suspended from the mandible, the tremor fr equency was unaltered; sharp taps delivered to the jaw did not elicit any kind of damped oscillations of the system. These findings indicate d the absence of mechanical resonance in the system. No correlation of the tremor signal with the electrocardiogram was found. However, a st rong correlation was found between the rectified electromyographic sig nals recorded over the masseter muscles and the tremor signal, where t he electromyographic signal preceded jaw movement by 20-30 msec. Frequ ency-domain analysis also showed positive peaks in a majority of coher ence functions between electromyographic and tremor signals. These res ults suggested a strong neurogenic component of the tremor. (C) 1998 E lsevier Science Ltd. All rights reserved.