Decisions under risk in Parkinson’s disease: Preserved evaluation of probability and magnitude

• Published in: Neuropsychologia Vol. 51; no. 13; pp. 2679 - 2689
• Main Authors: Sharp, Madeleine E., Viswanathan, Jayalakshmi, McKeown, Martin J., Appel-Cresswell, Silke, Stoessl, A. Jon, Barton, Jason J.S.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.11.2013; Elsevier
• Subjects: Adult and adolescent clinical studies; Aged; Antiparkinson Agents - pharmacology; Antiparkinson Agents - therapeutic use; Biological and medical sciences; Case-Control Studies; Decision Making - drug effects; Decision Making - physiology; Decision-making; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Disruptive, Impulse Control, and Conduct Disorders - etiology; Female; Games, Experimental; Humans; Impulse control disorders; Levodopa - pharmacology; Levodopa - therapeutic use; Male; Medical sciences; Middle Aged; Nervous system (semeiology, syndromes); Nervous system as a whole; Neurology; Organic mental disorders. Neuropsychology; Parkinson Disease - complications; Parkinson Disease - drug therapy; Parkinson Disease - psychology; Parkinson’s disease; Probability; Prospect theory; Psychology. Psychoanalysis. Psychiatry; Psychometrics; Psychopathology. Psychiatry; Risk-Taking; Decision-making; Prospect theory; Impulse control disorders; Parkinson’s disease; Human; Evaluation; Nervous system diseases; Impulse control disorder; Parkinson's disease; Decision making; Parkinson disease; Probability; Cognition; Risk taking; Cerebral disorder; Central nervous system disease; Degenerative disease; Elderly; Extrapyramidal syndrome
• ISSN: 0028-3932; 1873-3514
• DOI: 10.1016/j.neuropsychologia.2013.08.008

Unmedicated Parkinson’s disease patients tend to be risk-averse while dopaminergic treatment causes a tendency to take risks. While dopamine agonists may result in clinically apparent impulse control disorders, treatment with levodopa also causes shift in behaviour associated with an enhanced response to rewards. Two important determinants in decision-making are how subjects perceive the magnitude and probability of outcomes. Our objective was to determine if patients with Parkinson’s disease on or off levodopa showed differences in their perception of value when making decisions under risk. The Vancouver Gambling task presents subjects with a choice between one prospect with larger outcome and a second with higher probability. Eighteen age-matched controls and eighteen patients with Parkinson’s disease before and after levodopa were tested. In the Gain Phase subjects chose between one prospect with higher probability and another with larger reward to maximize their gains. In the Loss Phase, subjects played to minimize their losses. Patients with Parkinson’s disease, on or off levodopa, were similar to controls when evaluating gains. However, in the Loss Phase before levodopa, they were more likely to avoid the prospect with lower probability but larger loss, as indicated by the steeper slope of their group psychometric function (t(24)=2.21, p=0.04). Modelling with prospect theory suggested that this was attributable to a 28% overestimation of the magnitude of loss, rather than an altered perception of its probability. While pre-medicated patients with Parkinson’s disease show risk-aversion for large losses, patients on levodopa have normal perception of magnitude and probability for both loss and gain. The finding of accurate and normally biased decisions under risk in medicated patients with PD is important because it indicates that, if there is indeed anomalous risk-seeking behaviour in such a cohort, it may derive from abnormalities in components of decision making that are separate from evaluations of size and probability. •We compared risky decision-making in PD patients on and off levodopa and in controls.•PD patients are largely similar to controls in their decision-making.•Perception of probability and magnitude is normal across groups.•Only difference was that unmedicated PD avoid large losses.•According to prospect theory, this is due to overestimation of loss size.