Bidirectional modulation of reward-guided decision making by dopamine

The neuromodulator dopamine is known to play a key role in reward-guided decision making, where choice options are often characterized by multiple attributes. Different decision strategies can be used to merge these choice attributes with personal preferences (e.g. risk preferences) and integrate them into a single subjective value. While the influence of dopamine on risk preferences has been investigated, it is unknown whether dopamine is also involved in arbitrating between decision strategies. We investigated this using a reward-guided decision-making task which was performed by 31 healthy participants under the influence of the dopamine D2/D3-receptor antagonist amisulpride, the dopamine precursor L-DOPA, or placebo in a double-blind within-subject design. Notably, we observed that the dopaminergic interventions shifted the (overall) weighting of option attributes without changing how option attributes are integrated into a subjective value (decision strategy). These effects were bidirectional: Amisulpride reduced the degree to which choices were influenced by both reward magnitude and reward probability, whereas the opposite was observed under L-DOPA, where we found an increased effect of reward magnitude and reward probability on choice. These effects occurred in the absence of changes in statistically optimal behavior. Together, our data provide evidence for a role of dopamine in controlling the influence of value parameters on choice irrespective of decision strategies.