Dissociation of decision-making under ambiguity and decision-making under risk in patients with Parkinson's disease: a neuropsychological and psychophysiological study.

Decision-making impairments in Parkinson's disease (PD) are most likely associated with dysfunctions in fronto-striatal loops. Recent studies examined decision-making in PD either in ambiguous situations with implicit rules, using the Iowa Gambling Task (IGT), or in risky situations with explicit rules, using the Game of Dice Task (GDT). Both tasks have been associated with the limbic-orbitofrontal-striatal loop, involved in emotional processing. However, the GDT has additionally been highly associated with the dorsolateral prefrontal-striatal loop, being involved in executive functions. The present study is the first one which examined decision-making in PD patients with both, IGT and GDT. We studied 21 non-demented PD patients on dopaminergic medication and 23 healthy controls with both tasks and a neuropsychological test battery with focus on executive functions. To analyse possible abnormalities in emotional processing, electrodermal responses (EDRs) were assessed while performing the tasks. We found that PD patients were significantly impaired in the GDT, but not in the IGT. Executive dysfunctions correlated with GDT but not with IGT performance. In both tasks, PD patients showed significantly reduced feedback EDRs after losses, but not after gains, indicating a primary decline of sensitivity to negative feedback. Our behavioural data suggest that dysfunctions in the dorsolateral prefrontal loop might be stronger than in the limbic loop, resulting in deficits in executive functions and GDT performance but unimpaired IGT performance. Reduced sensitivity to negative feedback is discussed with regard to dysfunctions in the limbic loop, which may result from pathology of limbic structures or dopaminergic medication.