Intertemporal choice in Parkinson's disease and restless legs syndrome

•De novo Parkinson patients show steeper delay discounting than healthy controls.•Compared discounting functions across several groups of participants including restless legs and de novo patients.•Steeper discounting is likely a trait marker of Parkinson's disease.

BackgroundImpulse control disorders in Parkinson's disease are a potential consequence of dopaminergic therapy. Impulse control problems might be revealed by intertemporal choice tasks which entail to forgo an immediately available reward in favor of a larger but later reward. The steepness of the discounting curve can be quantified by the parameter k.MethodsParticipants (37 Parkinson patients [13 de novo, 24 medicated], 24 patients with restless legs syndrome, and 22 controls) were offered 54 choices between immediate smaller rewards and delayed larger and the k value was estimated from the participants' responses. Participants had the chance of winning one of their decisions. None of the participants had impulse control disorders.ResultsUnmedicated Parkinson patients had a higher discounting rate than controls and medicated patients with restless legs syndrome. The k values of medicated Parkinson patients and patients with restless legs syndrome did not differ from those of controls. No correlation was found between the k value and the dopamine agonist dose.ConclusionImpulsive decision making in patients with Parkinson's disease may occur as part of the disease rather than as a consequence of dopamine agonist therapy.