Impaired incentive learning in treated Parkinson's disease.
OBJECTIVE: To quantify the performance of patients with Parkinson's disease (PD) in incentive learning, or learning to respond to stimuli that signal the imminent presentation of a reinforcer, and in paired-associate learning, or learning of word associations. METHODS: The performance of 32 patients with idiopathic PD was compared to that of 25 healthy control subjects, and 32 subjects suffering from arthritis, matched for age and education. The PD and arthritic groups were comparable on a self-report measure of physical disability. All subjects were physically capable of satisfying the contingencies of the incentive learning task. The avoidance task that quantified incentive learning used money loss as an aversive stimulus. The word paired-associate learning task was presented on a computer and feedback was not given on performance. RESULTS: The normal and arthritic groups performed equally well on the avoidance task, whereas the PD group was impaired despite dopaminergic replacement therapy. The groups did not differ significantly in paired-associate learning. CONCLUSIONS: These findings are among the first to suggest that the nigrostriatal dopamine dysfunction associated with PD may play a role in incentive learning but not in paired-associate learning and are consistent with a role for dopamine in certain forms of learning and memory. The findings may highlight differences between tonic and modulated function in the nigrostriatal system.