The ability to assess muscular force in asymmetrical Parkinson's disease.

We tested the ability of eight Parkinson's disease (PD) patients with clearly asymmetrical right-sided motor signs and eight control subjects to assess different levels of muscular forces. In Experiment 1, subjects had first to produce a target-force with one hand (the reference hand) with the assistance of visual feedback, and then match that force with the other hand (the matching hand) without any visual feedback. In Experiment 2, they had to produce a target-force with one hand and then estimate it by attributing a numerical value. In Experiment 1, the results showed that PD patients could normally reach the target-forces with the more affected left hand but they were impaired in inter-manual force transfer. They were also impaired, in Experiment 2, in estimating forces produced by their more affected hand. Our findings suggest that PD patients present a deficit in sensing motor effort. Effort awareness might be mediated by the basal ganglia.