hide
Free keywords:
-
Abstract:
Objective:How we evaluate the suffering of others is a central concern in moral decision-making, but its neural basis is unknown. Here, we investigated how people value others’ pain relative to their own pain, and how serotonin and dopamine influence aversion topain for self and others. Methods:Two subjectsparticipated in each experimental session under conditions of complete anonymity and were randomly assigned to the roles of ‘Decider’ and ‘Receiver’. Deciders made a series of choices between a smaller amount of money plus a smaller number of mildly painful electric shocks, versus a larger amount of money plusa larger number of shocks. The Decider always received the money, but the shocks were allocated to the Decider on half of the trials and to the Receiver on the other half.We deployed this paradigm intwo behavioral studies (N = 39 and N = 41)and used acomputational model of Deciders’ choices to derive a pair of subject-specific harm aversion parameters that characterized the subjective cost of pain for self and others,respectively. We then carried out two double-blind, placebo-controlled pharmacological studiesto investigatethe effects of the serotonin reuptake inhibitor citalopram (N = 89) and the dopamine precursor levodopa (N = 86) on harm aversionfor self and others.Results:Across all four studies, we find that harm aversion for others is greater than harm aversion for self. In other words, most people will selflessly sacrifice more money to prevent others’ pain than their own pain. Citalopram and levodopa had distinct and opposing effects on moral decision-making: citalopram increased harm aversionfor both others and self, while levodopa selectively reduced harm aversion for otherswithout affecting harm aversion for self. Crucially, neither drug influenced the physical perceptionof pain, suggesting a direct influence of serotonin and dopamine on preferences.Conclusions:We show that serotonin and dopamine exert distinct effects on moral decision-making by differentially modulating the valuation of pain for self and others. Our findingshave implications forunderstanding antisocial behavior in psychiatric disordersassociated with abnormal serotonergic and dopaminergic function.
