Effector-specific visual information influences kinesthesis and reaction time performance in Parkinson's disease

Twelve patients diagnosed with idiopathic Parkinson's disease and 11 age-matched control participants performed a continuous bimanual wrist flexion-extension tracking task while vision of their hands was manipulated. Participants were required to match the frequency and amplitude of movements of 1 limb that was driven at 0.6 Hz by a torque motor by actively moving the contralateral limb. In half the trials, the more affected limb (subdominant for controls) was driven, and in the other half, the less affected limb (dominant for controls) was driven. Vision of both hands, vision of the driven hand only, vision of the active hand only, or no vision of the hands was allowed. Simple and probe reaction times were assessed. Parkinson's disease patients performed the tracking task to a reasonable level of temporal and spatial accuracy as compared with control participants in terms of hand phasing and root mean square error. Patients demonstrated a marked posture deviation (toward flexion), which was exaggerated when the less affected limb was active. Amplitude deviations were smaller in both groups when the less affected (dominant) limb was active and when participants had vision of the driven hand. Overall, patients delivered slower responses in both simple and probe conditions. Reaction times of Parkinson's disease patients who were allowed vision of only the active hand were longer than were those of patients in all other visual conditions, whereas visual conditions did not affect the reaction times of control participants. The authors conclude that central demands increase when movement regulation must be based solely on kinesthetic information and when vision directs attention away from the most relevant source of kinesthetic information.