Dopamine alters motor learning performance in the presence and absence of feedback

We often choose to learn motor skills not only because of some external reward, but also because motor learning, in and of itself, is satisfying. While dopamine is thought to drive reward-based motor learning, it remains unclear whether dopamine is implicated in motor learning under conditions ostensibly driven by intrinsic rewards/motivation (i.e., in the absence of extrinsic feedback or reward). Here, by pharmacologically manipulating dopamine using the dopamine precursor Levodopa, we investigated the role of dopamine in an explicit motor learning task guided by internally determined signals of performance success, by removing intrinsic feedback about task success. Specifically, we asked participants to strategically aim away from presented targets by various instructed angles: a form of explicit motor learning that contributes to performance in the classic visuomotor rotation task. In the feedback condition, targets jumped mid-movement by the instructed angle, such that success in target hitting depended on successfully aiming away by the instructed angle. In the no-feedback condition, intrinsic feedback about task success was removed by having targets disappear mid-movement, such that participants could not know if they succeeded at hitting the targets or not. We found that dopamine altered performance, both with and without task feedback about task success. This provides direct evidence for a role of dopamine in motor learning driven by internal task goals.