Abstract
Catecholamines modulate the impact of motivational cues on action. Such motivational biases have been proposed to reflect cue-based, 'Pavlovian' effects. Here, we assess whether motivational biases may also arise from asymmetrical instrumental learning of active and passive responses following reward and punishment outcomes. We present a novel paradigm, allowing us to disentangle the impact of reward and punishment on instrumental learning from Pavlovian response biasing. Computational analyses showed that motivational biases reflect both Pavlovian and instrumental effects: reward and punishment cues promoted generalized (in)action in a Pavlovian manner, whereas outcomes enhanced instrumental (un)learning of chosen actions. These cue- and outcome-based biases were altered independently by the catecholamine enhancer melthylphenidate. Methylphenidate's effect varied across individuals with a putative proxy of baseline dopamine synthesis capacity, working memory span. Our study uncovers two distinct mechanisms by which motivation impacts behaviour, and helps refine current models of catecholaminergic modulation of motivated action.
Highlights
Catecholamine transmission has long been implicated in key aspects of adaptive behaviour, including learning, action, and motivation
Including two Go response options enabled us to tease apart general activation/inhibition related to the Pavlovian response bias and specific action learning related to the instrumental learning bias using computational models and behavioural analyses
Because each Go and NoGo cues (Go cues) was associated with only one correct Go response, we confirmed that this motivational bias was present for both correct and incorrect Go responses
Summary
Catecholamine (i.e. dopamine and noradrenaline) transmission has long been implicated in key aspects of adaptive behaviour, including learning, action, and motivation. The neuromodulator dopamine has been linked strongly to behavioural activation in the context of reward (Taylor and Robbins, 1986; 1984), putatively by amplifying the perceived benefits of action over their costs (Collins and Frank, 2014; Niv et al, 2007). This behavioural activation to reward-predicting cues is likely to be, at least partly, Pavlovian in nature, with the conditioned cues eliciting innately specified responses (Figure 1A).
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