Phasic nucleus accumbens dopamine encodes risk-based decision-making behavior

Background: To optimize behavior, organisms evaluate the risks and benefits of available choices. The mesolimbic dopamine (DA) system encodes information about response costs and reward delays that bias choices. However, it remains unclear whether subjective value associated with risk-taking behavior is encoded by DA release.

Methods: Rats (n = 11) were trained on a risk-based decision-making task in which visual cues predicted the opportunity to respond for smaller certain (safer) or larger uncertain (riskier) rewards. Following training, DA release within the nucleus accumbens (NAc) was monitored on a rapid time scale using fast-scan cyclic voltammetry during the risk-based decision-making task.

Results: Individual differences in risk-taking behavior were observed as animals displayed a preference for either safe or risky rewards. When only one response option was available, reward predictive cues evoked increases in DA concentration in the NAc core that scaled with each animal's preferred reward contingency. However, when both options were presented simultaneously, cue-evoked DA release signaled the animals preferred reward contingency, regardless of the future choice. Furthermore, DA signaling in the NAc core also tracked unexpected presentations or omissions of rewards following prediction error theory.

Conclusions: These results suggest that the dopaminergic projections to the NAc core encode the subjective value of future rewards that may function to influence future decisions to take risks.