Abstract
Dopamine (DA) has been implicated in exploration-exploitation behaviour, i.e., exploring novel, potentially better options vs. exploiting known, previously rewarding options. Impairments in this trade-off occur in psychiatric disorders involving DAergic dysfunction, including addiction and schizophrenia. Pharmacological studies revealed a contribution of DA to exploration, but inconsistent findings suggest interindividual variability in baseline DA may modulate effects. To address this, we investigated the effects of the DA precursor L-DOPA on exploration-exploitation during reinforcement learning in N = 75 healthy participants (n = 32 women), following a randomised, double-blind, placebo-controlled, pre-registered design (
https://osf.io/p2r7u
). We assessed whether putative baseline DA markers, including spontaneous eye blink rate, working memory (WM) capacity, and impulsivity, modulated drug effects and examined visual fixation patterns and pupil dilation. L-DOPA had no overall effect on computational model parameters of random exploration, directed exploration or choice perseveration. WM capacity moderated drug effects on random exploration, with stronger effects at higher WM capacity. Remaining DA proxies showed no credible effects. Pooling male participant data with that from an earlier male-only study (Chakroun et al., 2020; total N = 74), L-DOPA increased uncertainty-dependent value weighting and perseveration strength. No credible drug effects were observed in female participants. Pupil dilation was tonically increased under L-DOPA and scaled with exploration behaviour and prediction error, confirming that pupillometry can index exploration dynamics. Visual exploration patterns reflected uncertainty-driven sampling, but were unaffected by L-DOPA. Results suggest that DAergic modulation of exploration and perseveration may be contingent on cognitive capacity and sex, rather than exerting uniform effects.
Significance statement
Dopamine regulates the balance between exploring new opportunities and exploiting known rewards, often altered in disorders involving dopaminergic dysfunction, such as addiction and schizophrenia. However, pharmacological studies have produced mixed findings, suggesting dopamine's effects may vary across individuals. In a randomised, double-blind, placebo-controlled study, L-DOPA had no overall effect on exploration, while working memory capacity moderated drug effects on random exploration. Pooling male participants with a previous male-only study, L-DOPA increased choice perseveration and uncertainty-dependent value weighting. Visual fixations reflected uncertainty-guided information sampling, while pupil dilation tracked exploration-related computations. These findings help reconcile prior findings and highlight the importance of individual differences in dopaminergic modulation of decision-making.