Cue-Evoked Dopamine Neuron Activity Helps Maintain but Does Not Encode Expected Value

Summary: Cue-evoked midbrain dopamine (DA) neuron activity reflects expected value, but its influence on reward assessment is unclear. In mice performing a trial-based operant task, we test if bidirectional manipulations of cue or operant-associated DA neuron activity drive learning as a result of under- or overexpectation of reward value. We target optogenetic manipulations to different components of forced trials, when only one lever is presented, and assess lever biases on choice trials in the absence of photomanipulation. Although lever biases are demonstrated to be flexible and sensitive to changes in expected value, augmentation of cue or operant-associated DA signaling does not significantly alter choice behavior, and blunting DA signaling during any component of the forced trials reduces choice trial responses on the associated lever. These data suggest cue-evoked DA helps maintain cue-value associations but does not encode expected value as to set the benchmark against which received reward is judged. : Although reward-predictive cues increase midbrain dopamine neuron activity in proportion to the expected value of the anticipated reward, Mendoza et al. demonstrate that cue-evoked dopamine does not prospectively encode expected value as to influence reward assessment. Rather, cue-evoked dopamine is important for the maintenance of cue-value associations. Keywords: dopamine, ventral tegmental area, expected value, reinforcement learning, reward prediction error, overexpectation, motivation, optogenetics, calcium imaging