Methods of time and frequency domain examination of physiological tremor in the human jaw

This paper discusses, using the human jaw as a model, some of the commonly used techniques for examining physiological tremor. The EMG component driving mandibular physiological tremor ∼7 Hz can be revealed in the time domain manifestation of EMG by demodulation. The co-occurrence of ∼7 Hz physiological tremor (PT) in force and EMG can also be seen in the frequency domain representations of these signals and coherence analysis provides a method by which the degree of co-occurrence can be statistically investigated. Additionally, estimation of time lags between the signals by phase and cumulant density analysis provides evidence of the direction of dependence. Data presented herein using these techniques illustrates that for the human jaw, PT arises from a rhythmic component of EMG. This component is frequency and amplitude invariant across a range of bite forces indicating that it is not due to interaction between the stretch reflex and the mechanical resonance of the system.