Abstract
RationaleBrain catecholamines have long been implicated in reinforcement learning, exemplified by catecholamine drug and genetic effects on probabilistic reversal learning. However, the mechanisms underlying such effects are unclear.Objectives and methodsHere we investigated effects of an acute catecholamine challenge with methylphenidate (20 mg, oral) on a novel probabilistic reversal learning paradigm in a within-subject, double-blind randomised design. The paradigm was designed to disentangle effects on punishment avoidance from effects on reward perseveration. Given the known large individual variability in methylphenidate’s effects, we stratified our effects by working memory capacity and trait impulsivity, putatively modulating the effects of methylphenidate, in a large sample (n = 102) of healthy volunteers.ResultsContrary to our prediction, methylphenidate did not alter performance in the reversal phase of the task. Our key finding is that methylphenidate altered learning of choice-outcome contingencies in a manner that depended on individual variability in working memory span. Specifically, methylphenidate improved performance by adaptively reducing the effective learning rate in participants with higher working memory capacity.ConclusionsThis finding emphasises the important role of working memory in reinforcement learning, as reported in influential recent computational modelling and behavioural work, and highlights the dependence of this interplay on catecholaminergic function.
Highlights
IntroductionBrain catecholamines (dopamine and noradrenaline) are well known to play a fundamental role in reinforcement learning and decision-making
Brain catecholamines are well known to play a fundamental role in reinforcement learning and decision-making
Subsequent studies in young healthy volunteers have shown that administration of the dopamine transporter blocker methylphenidate to healthy volunteers modulates reversal-related BOLD signal in the striatum (Dodds et al 2008) and impaired reversal learning in proportion to the degree that methylphenidate increased striatal dopamine release (Clatworthy et al 2009)
Summary
Brain catecholamines (dopamine and noradrenaline) are well known to play a fundamental role in reinforcement learning and decision-making. Subsequent studies in young healthy volunteers have shown that administration of the dopamine (and noradrenaline) transporter blocker methylphenidate to healthy volunteers modulates reversal-related BOLD signal in the striatum (Dodds et al 2008) and impaired reversal learning in proportion to the degree that methylphenidate increased striatal dopamine release (Clatworthy et al 2009). While these studies establish a causal role for striatal dopamine in reversal learning, the mechanism by which dopamine alters the ability to reverse responding remains unclear
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