Rationale: Evaluation of risks and rewards associated with different options is facilitated by components of the mesocorticolimbic dopamine (DA) system. Augmenting or reducing DA activity increases or decreases preference for larger, uncertain rewards when reward probabilities decrease within a session. However, manipulations of DA activity may differentially alter risky choice when shifts in the relative value of probabilistic rewards are greater or lesser than those experienced previously.
Objectives: We investigated the effects of amphetamine and the DA antagonist flupenthixol on risk discounting, whereby we altered the manner in which reward probabilities changed.
Methods: Rats chose between a "Small/Certain" (one pellet) and a "Large/Risky" lever that delivered four pellets in a probabilistic manner that changed during a session. Separate groups of rats were trained with a descending (100%, 50%, 25%, 12.5%), ascending (12.5-100%) or mixed (100%, 12.5%, 25%, 50%) order of probabilities associated with the large/risky option.
Results: Flupenthixol consistently decreased preference for the large/risky option. In contrast, amphetamine increased preference for the large/risky lever when the probabilities decreased over a session, but reduced preference in the ascending condition.
Conclusions: Reductions in normal DA tone consistently biases choice away larger, probabilistic rewards. In contrast, increases in DA release may disrupt adjustments in behavior in response to changes in the relative value of certain versus uncertain rewards. These findings further clarify the role of DA in mediating risk/reward judgments and how perturbations in DA signaling may interfere with the ability to adjust decision making in response to changes in reward contingencies.