Bar color indicates correlation between dopamine and reward rate. n=51 probe locations, from 12 rats, each with two microdialysis probes that were lowered between sessions. c, Top, microdialysis locations in medial frontal cortex and striatum (see also Extended Data Fig.1). Bottom, NAc core dopamine in the same session (1 min samples). Next row, leaky-integrator estimate of reward rate (black) and running-average of latency (cyan inverted log scale). Top row, reward probabilities in each block (left:right) Next row, ticks indicate outcome of each trial (tall, rewarded short, unrewarded). Our primary conclusion is that although RPE-scaled VTA dopamine spike bursts provide abrupt changes in dopamine release appropriate for learning, separate NAc dopamine fluctuations associated with motivation arise independently from VTA dopamine cell firing.ĭopamine release covaries with reward rate specifically in NAc core and ventral prelimbic cortex.Ī, Bandit task events. To measure NAc dopamine release we used three independent methods – microdialysis, voltammetry, and the optical sensor dLight 15 – with convergent results. We identified VTA dopamine neurons using optogenetic tagging 3, 14. We therefore compared firing with release under the same conditions. With few exceptions 2, 13, 14, midbrain dopamine firing has been examined during classical conditioning in head-fixed animals 3, 12, unlike forebrain dopamine release. Furthermore, NAc dopamine escalates during motivated approach, consistent with encoding value, 7– 11. But they also affect motivated behaviors immediately, as if dopamine signals reward expectation (value) 5. Dopamine manipulations can affect learning as if altering RPEs 4– 6. Brief increases in dopamine cell firing encode reward prediction errors (RPEs 1– 3) - learning signals for optimizing future motivated behavior. Our results suggest a fundamental difference in how dopamine release is regulated to achieve distinct functions: broadcast burst signals promote learning, while local control drives motivation.ĭopamine is famously related to “reward” – but how exactly? One function involves learning from unexpected rewards. Yet NAc core dopamine release also covaried with dynamically-evolving reward expectations, without corresponding changes in VTA dopamine cell spiking. Cues indicating upcoming reward increased both spiking and release. Here we compare spiking of identified VTA dopamine cells with NAc dopamine release in the same decision-making task. This mismatch might reflect differences in behavioral tasks, slower changes in dopamine cell spiking, or spike-independent modulation of dopamine release. By contrast, dopamine release ramps up as animals approach rewards, mirroring reward expectation. Dopamine spiking can encode prediction errors, vital learning signals in computational theories of adaptive behavior. How dopamine supports both functions is unclear. The dopamine projection from ventral tegmental area (VTA) to nucleus accumbens (NAc) is critical for motivation to work for rewards, and reward-driven learning.
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