Dopaminergic modulation of the sense of agency influences moral behavior in Parkinson's disease.

Abstract

Embodied accounts of morality propose that corporeal self-awareness helps restrain immoral actions. The Sense of Agency (SoA)-the feeling of controlling one's actions and their consequences-drops when individuals harm others. However, whether modulating SoA shifts moral behavior remains unclear. Parkinson's Disease (PD) offers a unique model to address this question, because dopaminergic dysfunction affects both SoA and moral decision-making. We tested 23 individuals with PD in ON and OFF dopaminergic state, and 24 healthy controls using two tasks assessing SoA (SoA-GAME) and moral decision-making (Temptation to Lie Card Game, TLCG), respectively. The SoA-GAME quantified perceived synchrony between executed and observed virtual actions, indexing SoA changes driven by action-related prediction errors (PEs). The TLCG measures self-serving dishonesty by tempting participants to deceive another player for monetary gain. Dopaminergic medication increased SoA relative to OFF state-especially when virtual movements matched participants' movements but failed to achieve the intended goal-and was associated with reduced dishonest behavior. Drift diffusion modeling showed that dopaminergic state modulated the accumulation of evidence underlying agency judgments, specifically in response to action-related PEs. Critically, higher perceived synchrony in the SoA-GAME predicted a reduction of dishonest choices, but only when individuals with PD were tested ON dopaminergic medication. These findings indicate that dopaminergic modulation of SoA and of the action-related PEs that inform it can influence moral behavior, supporting a direct connection between corporeal self-awareness and morality.