Action Tremor During Object Manipulation in Parkinson’s Disease

Summary: In previous studies of fingertip forces during pre-cision grip in subjects with Parkinson’s disease (PD), we ob-served regular oscillations in isometric force. The present study characterizes the nature of these oscillations. Fingertip forces were recorded from the index finger and thumb during preci-sion grip-lifts with a 300 g and 900 g object in 10 subjects with PD and 20 healthy control subjects. Fourier analysis confirmed that all subjects with PD exhibited force oscillations with a clearly definable frequency ( ~ 7–11 Hz). Five of these subjects also exhibited a second lower frequency peak ( ~ 5 Hz). Ap-proximately half of the 20 control subjects displayed a single frequency peak ( ~ 8–12 Hz), which was generally lower in am-plitude than in the subjects with PD (representing enhanced physiological tremor), whereas the remaining control subjects had low-amplitude, broad-based spectra (representing physi