Bilateral tremor relations in Parkinson's disease: effects of mechanical coupling and medication.

The aim of the present study was to examine the dynamics of bilateral multiple segment resting and postural tremor in 12 young, older subjects and eight Parkinson's (PD) patients in their different medication states. A second aim was to investigate whether bilateral independence of upper limb tremor was preserved for PD patients with amplified tremor under conditions where no upper limb segment was supported. Under these conditions, the likelihood for mechanical transmission between segments was increased. Tremor was recorded, bilaterally, from the hand and finger segments of all subjects. In addition to the PD subjects exhibiting greater tremor under both on/off medication states than the young/old control subjects, the tremor increase within limb from the hand to the finger was 2-3 times greater for the PD group in comparison to the healthy subjects. Despite this increased tremor, no differences were observed in the level of coupling between limbs across groups. Furthermore, the degree of coupling between limbs for the PD group was unaffected by their medication state. Overall, these results demonstrate that bilateral independence of tremor in PD participants is preserved despite conditions which maximised the chance of increased coupling.