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The role dopamine plays in decision-making has important theoretical, empirical and clinical implications. Here, we examined its precise contribution by exploiting the lesion deficit model afforded by Parkinson's disease. We studied patients in a two-stage reinforcement learning task, while they were ON and OFF dopamine replacement medication. Contrary to expectation, we found that dopaminergic drug state (ON or OFF) did not impact learning. Instead, the critical factor was drug state during the performance phase, with patients ON medication choosing correctly significantly more frequently than those OFF medication. This effect was independent of drug state during initial learning and appears to reflect a facilitation of generalization for learnt information. This inference is bolstered by our observation that neural activity in nucleus accumbens and ventromedial prefrontal cortex, measured during simultaneously acquired functional magnetic resonance imaging, represented learnt stimulus values during performance. This effect was expressed solely during the ON state with activity in these regions correlating with better performance. Our data indicate that dopamine modulation of nucleus accumbens and ventromedial prefrontal cortex exerts a specific effect on choice behaviour distinct from pure learning. The findings are in keeping with the substantial other evidence that certain aspects of learning are unaffected by dopamine lesions or depletion, and that dopamine plays a key role in performance that may be distinct from its role in learning.

Original publication

DOI

10.1093/brain/aws083

Type

Journal article

Journal

Brain : a journal of neurology

Publication Date

06/2012

Volume

135

Pages

1871 - 1883

Addresses

Wellcome Trust Centre for Neuroimaging, UCL, London, WC1N 3BG, UK. tamarashiner@gmail.com

Keywords

Nucleus Accumbens, Prefrontal Cortex, Humans, Parkinson Disease, Oxygen, Levodopa, Carbidopa, Dopamine Agents, Drug Combinations, Magnetic Resonance Imaging, Photic Stimulation, Association Learning, Generalization (Psychology), Reinforcement (Psychology), Choice Behavior, Psychomotor Performance, Dose-Response Relationship, Drug, Image Processing, Computer-Assisted, Adult, Aged, Aged, 80 and over, Middle Aged, Female, Male