Dopamine D2-receptor blockade in humans disrupts the effect of effort on learning

Humans and other animals learn the value of candidate actions by interacting with their environment, which invariably requires the exertion of effort. Dopamine has been implicated in both effort and reward learning, but little is known about how these processes interact. In this double-blind study, healthy young adults (N = 42) were randomized to receive either high-dose sulpiride (a post-synaptic D2-receptor antagonist) or placebo. Participants then completed a novel two-armed bandit task, in which they weighed the effort costs associated with each option against their expected rewards. Overall, learning accuracy was lower on sulpiride compared to placebo. Computational modeling revealed that this was driven by the capacity of effort to significantly modulate learning rates on placebo but, critically, not on sulpiride. Simulations showed that the capacity of effort to modulate learning rates plays an adaptive role by improving performance in agents whose learning would otherwise be compromised by low motivation. Together, these data provide causal evidence that dopamine supports the relationship between effort and learning, and reveal a novel role for dopamine in shaping how humans learn from the consequences of their actions.