Cognitive control is effortful, causing people to avoid demanding tasks, and undermining goal-directed behavior. Striatal dopamine promotes physical effort for reward, by increasing sensitivity to reward benefits and decreasing sensitivity to effort costs. These results, along with evidence that the costs of cognitive effort are encoded in cortico-striatal circuits, raise the possibility that striatal dopamine could boost motivation for cognitive effort as well. We hypothesised that striatal dopamine shapes both the learning and the expression of policies governing cost-benefit tradeoffs and our willingness to exert cognitive effort.

This talk describes two studies respectively investigating how striatal dopamine impacts on effort learning and decision-making. Our studies combined [18F]-DOPA PET imaging of dopamine synthesis capacity with dopamine transport blocker methylphenidate, the D2 agent sulpiride, and placebo. In one study, participants decided between doing harder working memory tasks for more money or easier tasks for less money. We find that willingness to expend cognitive effort depends on baseline striatal dopamine function, and that dopaminergic drugs can also boost motivation for those with low dopamine synthesis capacity. In another study, participants learned stimulus-response associations in a task which dissociates the contributions of reinforcement learning and working memory to behaviour. We find that greater dopamine signaling increases the degree to which people rely on costly working memory versus cheap reinforcement learning and also that methylphenidate blunts effort discounting during reinforcement learning.