title: Assaying the effect of levodopa on the evaluation of risk in healthy humans.
abstract: In humans, dopamine is implicated in reward and risk-based decision-making. However, the specific effects of dopamine augmentation on risk evaluation are unclear. Here we sought to measure the effect of 100 mg oral levodopa, which enhances synaptic release of dopamine, on choice behaviour in healthy humans. We use a paradigm without feedback or learning, which solely isolates effects on risk evaluation. We present two studies (n = 20; n = 20) employing a randomised, placebo-controlled, within-subjects design. We manipulated different dimensions of risk in a controlled economic paradigm. We test effects on risk-reward tradeoffs, assaying both aversion to variance (the spread of possible outcomes) and preference for relative losses and gains (asymmetry of outcomes--skewness), dissociating this from potential non-specific effects on choice randomness using behavioural modelling. There were no systematic effects of levodopa on risk attitudes, either for variance or skewness. However, there was a drift towards more risk-averse behaviour over time, indicating that this paradigm was sensitive to detect changes in risk-preferences. These findings suggest that levodopa administration does not change the evaluation of risk. One possible reason is that dopaminergic influences on decision making may be due to changing the response to reward feedback.
authors.affiliation: Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, London, United Kingdom. mkael.symmonds@googlemail.com
authors.forename: Mkael
authors.initials: M
authors.lastname: Symmonds
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Wright
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Fagan
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Dolan
mesh_terms: D000293:Adolescent; D000328:Adult; D000465:Algorithms; D000978:Antiparkinson Agents / Q000008:administration & dosage / Q000494:pharmacology*; D003657:Decision Making / Q000187:drug effects*; D005260:Female; D005715:Gambling; D006801:Humans; D007980:Levodopa / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D008960:Models, Psychological; D012201:Reward; D012309:Risk-Taking; D055815:Young Adult
chemical_list: D000978:Antiparkinson Agents; D007980:Levodopa