It has been well documented that Parkinson's disease (PD) patients are strongly dependent on visual feedback for online guidance of their movements, perhaps due to an impairment in proprioceptive integration. It is unknown, however, if PD patients are able switch between dominant (visual) and non- dominant (proprioceptive) sources of sensorimotor information when forced to do so. Furthermore, the role of visual feedback in the ability to generate a mental representation of the intended movement has not been systematically manipulated. It is postulated that PD produces abnormally noisy basal ganglia output, which diminishes the ability of PD patients to adequately integrate proprioceptive feedback in the representation of the intended movement, thus necessitating visual online monitoring. This dependence on visual feedback and online monitoring may be a contributor to bradykinetic movements in PD patients, one of the debilitating features of the disease. The proposed series of experiments will methodically manipulate visual and proprioceptive feedback during pointing movements of PD patients and age-matched healthy controls to determine the ability of PD patients to use alternative, or multiple sources of sensorimotor information. The systematic and novel methodology of the proposed experiments will elucidate the various contributions of multiple sources of sensorimotor information in pointing movements of PD patients. The data obtained will be useful towards isolating the various sensorimotor impairments with PD, allowing for inferences to be made regarding the role of the basal ganglia in motor control.
