Dopamine dependent reaction time deficits in patients with Parkinson's disease are task specific.

This study tested the hypothesis that patients with Parkinson's disease are impaired when they must rely on internal information to generate a response. Choice reaction times of control subjects and patients with Parkinson's disease, on and off their medication, were measured in tasks in which the motor demands were constant but which varied in the degree to which the stimuli held intrinsic information about the required response. A dopaminergic deficit was observed only in the tasks which employed stimuli compatible with the response and not in a task employing stimuli arbitrarily associated with the response. The data do not support the hypothesis that patients are differentially impaired in using internalized stimulus-response relationships.