A mismatch between kinesthetic and visual perception in Parkinson's disease.

Kinesthesia may be defective in patients with Parkinson's disease (PD), and this defect conceivably has a role in parkinsonian hypokinetic symptoms. In the present study, PD patients used kinesthetic perception to estimate the amplitude of passive angular displacements of the index finger about the metacarpophalangeal joint and to scale them as a percentage of a reference stimulus. The reference stimulus was either a standard kinesthetic stimulus preceding each test stimulus (task K) or a visual representation of the standard kinesthetic stimulus (task V). In task V, the PD patients' underestimation of the amplitudes of finger perturbations was significantly greater than that of normal subjects, but not for task K. PD patients' underestimation was also greater in task V than in task K; the difference between the underestimations was significantly greater than for normal subjects. These results suggest that, when kinesthesia is used to match a visual target, distances are perceived to be shorter by the PD patients. Assuming that visual perception is normal, kinesthesia is "reduced" in PD patients. This reduced kinesthesia, when combined with the well-known reduced motor output and probably reduced corollary discharges, implies that the sensorimotor apparatus is "set" smaller in PD patients than in normal subjects.