Temporally restricted dopaminergic control of reward-conditioned movements

Midbrain dopamine (DA) neurons encode both reward and movement-related events, and are implicated in disorders of reward processing as well as movement. Consequently, disentangling the contribution of DA neurons in reinforcing versus generating movements is challenging and has led to lasting controversy. We dissociated these functions by parametrically varying the timing of optogenetic manipulations in a Pavlovian conditioning task, and examining the influence on anticipatory licking prior to reward delivery. Inhibiting both ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) DA neurons in the post-reward period had a significantly greater behavioral effect than inhibition in the pre-reward period of the task. Furthermore, the contribution of DA neurons to behavior decreased linearly as a function of elapsed time after reward. Together, the results indicate a temporally restricted role of DA neurons primarily related to reinforcing stimulus-reward associations, and suggest that directly generating movements is a comparatively less important function.