Our device is optimized to measure wrist tone by passively pronating and supinating the subject’s hand utilizing a torque motor. Rigidity is expressed as the physiological frictional force opposing the movement of the motor at each angular position. Measurements are taken at a sampling rate of 482 Hz with 0.2 deg angular resolution and <10 mNm tone resolution (typical absolute tone increases in PD range from 50 to more than 200 mNm).

A pilot validation study demonstrated that our device successfully measured the increase in wrist tone between patients and healthy control subjects (55 ± 24 mNm, p=0.003, N=(4,6), unpaired ³Ù­-³Ù±ð²õ³Ù), as well as the changes in tone resulting from treatment with levodopa and deep brain stimulation. Our measurements agreed well with the UPDRS part III tone scores (linear regression, beta = 49 mNm, p < 1E-4, R^2=0.79).

Here we introduce a novel instrument for robust and accurate measurement of wrist rigidity. This platform will facilitate the study of neurophysiology state-dependent properties of wrist tone among Parkinson’s patients.