Phasic Nucleus Accumbens Dopamine Release Encodes Effort- and Delay-Related Costs

BackgroundOptimal decision-making requires that organisms correctly evaluate both the costs and benefits of potential choices. Dopamine transmission within the nucleus accumbens (NAc) has been heavily implicated in reward-learning and decision-making, but it is unclear how dopamine release might contribute to decisions that involve costs.MethodsCost-based decision-making was examined in rats trained to associate visual cues with either immediate or delayed rewards (delay manipulation) or low-effort or high-effort rewards (effort manipulation). After training, dopamine concentration within the NAc was monitored on a rapid time scale with fast-scan cyclic voltammetry.ResultsAnimals exhibited a preference for immediate or low-effort rewards over delayed or high-effort rewards of equal magnitude. Reward-predictive cues but not response execution or reward delivery evoked increases in NAc dopamine concentration. When only one response option was available, cue-evoked dopamine release reflected the value of the future reward, with larger increases in dopamine signaling higher-value rewards. In contrast, when both options were presented simultaneously, dopamine signaled the better of two options, regardless of the future choice.ConclusionsPhasic dopamine signals in the NAc reflect two different types of reward cost and encode potential rather than chosen value under choice situations.