From Prediction to Action: Dissociable Roles of Ventral Tegmental Area and Substantia Nigra Dopamine Neurons in Instrumental Reinforcement

Abstract

Reward-seeking requires the coordination of motor programs to achieve goals. Midbrain dopamine neurons are critical for reinforcement and their activation is sufficient for learning about cues, actions, and outcomes. Here we examine in detail the mechanisms underlying the ability of ventral tegmental area (VTA) and substantia nigra (SNc) dopamine neurons to support instrumental learning. By exploiting numerous behavioral tasks in combination with time-limited optogenetic manipulations, we reveal that VTA and SNc dopamine neurons generate reinforcement through separable psychological processes. VTA dopamine neurons imbue actions and their associated cues with motivational value that allows flexible and persistent pursuit whereas SNc dopamine neurons support time-limited, precise, action-specific learning that is non-scalable and inflexible. This architecture is reminiscent of actor-critic reinforcement learning models with VTA and SNc instructing the critic and actor, respectively. Our findings indicate that heterogeneous dopamine systems support unique forms of instrumental learning that ultimately result in disparate reward-seeking strategies.