Competing value signals impair reward-learning via dopaminergic mechanisms and increase exploration.

Effective reinforcement learning requires balancing exploration of uncertain options with exploitation of known outcomes. In real-world contexts, the same action may yield rewards in some situations and punishments in others, yet how these learning processes influence each other remains unclear. Here, we examine the neural mechanisms underlying how reward and punishment learning interact to guide adaptive behavior. We conducted four experiments (N = 159) using an instrumental learning task with binary choices, some of which were exclusive to reward or punishment learning trials, while others appeared in both, allowing assessment of their interaction. When choices were tied to a single learning type, reward learning engages less exploration (i.e., fewer choices of lower-value options) than punishment learning. Critically, when both learning processes were concurrently engaged, reward learning was selectively impaired, accompanied by enhanced exploration and greater activation in exploration-related prefrontal regions revealed by fMRI. Computational modeling showed that impaired reward learning was best explained by sensitivity to prior punishment history associated with reward-learning options, while individual differences in loss aversion predicted the degree of increased exploration. Finally, pharmacological attenuation of dopaminergic signaling via the D2/3 receptor antagonist amisulpride abolished both the increased exploration and the interference with reward learning. These findings suggest that punishment-history interference during reward learning is dopamine-modulated and associated with increased exploration, with individual differences in this exploration linked to loss aversion, providing a mechanistic account of how the brain resolves competing value signals and informing dopamine-related learning disturbances in neuropsychiatric conditions.