Serotonin selectively influences moral judgment and behavior through effects on harm aversion

Abstract

Aversive emotional reactions to real or imagined social harms infuse moral judgment and motivate prosocial behavior. Here, we show that the neurotransmitter serotonin directly alters both moral judgment and behavior through increasing subjects' aversion to personally harming others. We enhanced serotonin in healthy volunteers with citalopram (a selective serotonin reuptake inhibitor) and contrasted its effects with both a pharmacological control treatment and a placebo on tests of moral judgment and behavior. We measured the drugs' effects on moral judgment in a set of moral 'dilemmas' pitting utilitarian outcomes (e.g., saving five lives) against highly aversive harmful actions (e.g., killing an innocent person). Enhancing serotonin made subjects more likely to judge harmful actions as forbidden, but only in cases where harms were emotionally salient. This harm-avoidant bias after citalopram was also evident in behavior during the ultimatum game, in which subjects decide to accept or reject fair or unfair monetary offers from another player. Rejecting unfair offers enforces a fairness norm but also harms the other player financially. Enhancing serotonin made subjects less likely to reject unfair offers. Furthermore, the prosocial effects of citalopram varied as a function of trait empathy. Individuals high in trait empathy showed stronger effects of citalopram on moral judgment and behavior than individuals low in trait empathy. Together, these findings provide unique evidence that serotonin could promote prosocial behavior by enhancing harm aversion, a prosocial sentiment that directly affects both moral judgment and moral behavior. morality | punishment | ultimatum game | empathy | emotion

I fear for you: A role for serotonin in moral behavior

“…In addition, abnormal lack of empathy and amoral conduct of individuals with antisocial personality disorders impose considerable distress on their social environment, underscoring the need for effective pharmacological treatments to complement existing cognitive-behavioral approaches. Consistent with the observations of prior studies (10), the work by Crockett et al (4) suggests that serotonin augmentation might be a promising strategy to increase the emotional response of the amygdala and associated structures in individuals with social dysfunction. As illustrated by the emerging clinical success story of oxytocin (18,19), the strategy to translate pharmacological results guided by social neuroscience to clinical therapy holds considerable promise.…”

“…This is consistent with the interpretation that increased serotonin made subjects more likely to tolerate behavior that violates an ethical imperative (fairness) because punishing it would have (financially) harmed fellow coplayers. With these convergent observations, the study by Crockett et al (4) demonstrates that enhanced serotonin biases moral judgment and decision making toward sociality.…”

Impaired Decoding of Fear and Disgust Predicts Utilitarian Moral Judgment in Alcohol-Dependent Individuals

“…Specifically, impaired fear decoding emerged as the main predictor of utilitarian choices for high-conflict dilemmas, whereas impaired disgust decoding emerged as the main predictor of utilitarian choices for low-conflict dilemmas. Although future work is required to explore these effects, we suggest that the perception of fear in specific individuals may lead to an aversion to harming those individuals even when doing so may lead to saving other people, as in high-conflict scenarios (Crockett et al, 2010). On the other hand, low-conflict scenarios (e.g., causing harm for selfish benefit) may trigger moral disgust (Ugazio et al, 2012;Wheatley and Haidt, 2005).…”

Effects of Escitalopram Administration on Face Processing in Intermittent Explosive Disorder: An fMRI Study

“…In addition, serotonin dysfunction affects social cognition and behavior; for instance, animal research has shown that serotonin suppresses reactive aggression and promotes affiliate actions linked to social status in primates (Dayan and Huys, 2009). Moreover, human research has shown that tryptophan depletion (that decreases 5-HT availability) reduces cooperative behavior in a prisoner's dilemma game (Wood et al, 2006), whereas citalopram administration made subjects more likely to judge harmful actions as forbidden (Crockett et al, 2010) and enhanced reward sensitivity to facial expressions of a social partner (Tse et al, 2014). FMRI studies have found that citalopram reduces negative self-referential processing in depressed patients by enhancing medial PFC activity (Di Simplicio et al, 2012), and normalizes resting-state connectivity with the dorsal medial PFC (McCabe et al, 2011).…”