Uniform frequency of parkinsonian resting tremor in the lips, jaw, tongue, and index finger.

Parkinsonian resting tremor was examined in the lips, jaw, tongue, and index finger using electromyography (EMG) and displacement transduction. Long-term spectral averaging of tremor movement and EMG signals revealed that resting tremor frequencies were remarkably uniform across these orofacial and hand structures within the same parkinsonian subjects. However, marked variability in tremor spectral amplitude across structures and subtle moment-to-moment variations in tremor period, amplitude, and waveform shape were also observed. Although these observations argue for a central source of tremor, it appears that interactive central and/or peripheral neural circuitry may yield variations in tremor characteristics.