Serotonin selectively influences moral judgment and behavior through effects on harm aversion.
Level 2 - randomized trial
Controlled experimental pharmacological trial comparing an intervention to active and placebo controls in humans
PubMed 20876101 · doi:10.1073/pnas.1009396107
What was done
Healthy volunteers received acute serotonin enhancement via citalopram, a pharmacological control treatment, or a placebo. Investigators evaluated the effects on moral judgment using moral dilemmas pitting utilitarian outcomes against emotionally salient harmful actions, and on behavior using an ultimatum game measuring the acceptance or rejection of unfair financial offers. Responses were analyzed in relation to baseline trait empathy.
What was found
The abstract reports no numerical values, effect sizes, or test statistics. Directionally, citalopram significantly increased the likelihood of judging harmful actions as forbidden exclusively when harms were emotionally salient. In the ultimatum game, citalopram reduced the rejection rate of unfair offers. These harm-avoidant and prosocial shifts were moderated by personality traits, showing stronger magnitude in individuals with higher baseline trait empathy.
Why it matters
This study demonstrates a neurochemical mechanism underlying moral judgment, suggesting that serotonin selectively promotes prosocial choices by enhancing aversion to causing direct harm rather than by enforcing abstract fairness rules.
Limits
The abstract omits sample size, participant demographics, dosing, and whether the design was parallel or crossover. The outcomes rely on hypothetical moral dilemmas and economic laboratory games rather than real-world social behavior, and findings from acute SSRI administration in healthy volunteers may not reflect chronic effects or clinical populations.
Cited by
- contradicts Research by Molly Crockett demonstrated that depleting serotonin reduces prosocial and altruistic behavior.