Department of Experimental Psychology, Behavioural and Clinical Neuroscience Institute, University of Cambridge, Cambridge CB2 3EB, United Kingdom.
Proc Natl Acad Sci U S A. 2010 Oct 5;107(40):17433-8. doi: 10.1073/pnas.1009396107. Epub 2010 Sep 27.
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.
对真实或想象中的社会伤害产生厌恶情绪会影响道德判断，并促使亲社会行为的产生。在这里，我们表明，神经递质血清素通过增加受试者对伤害他人的厌恶感，直接改变道德判断和行为。我们通过西酞普兰（一种选择性血清素再摄取抑制剂）来增强健康志愿者的血清素水平，并将其对道德判断和行为的影响与药物对照治疗和安慰剂进行对比。我们在一系列道德“困境”中衡量了药物对道德判断的影响，这些困境将功利主义的结果（例如，拯救五条生命）与高度令人厌恶的有害行为（例如，杀死一个无辜的人）进行了对比。增强血清素使受试者更有可能判断有害行为是被禁止的，但前提是伤害是情感上明显的。在最后通牒博弈中，西酞普兰后也表现出这种回避伤害的偏见，在这种博弈中，受试者决定接受或拒绝另一个玩家的公平或不公平的金钱提议。拒绝不公平的提议可以执行公平规范，但也会对其他玩家造成经济损失。增强血清素会使受试者更不愿意拒绝不公平的提议。此外，西酞普兰的亲社会效应还与特质同理心有关。特质同理心高的个体比特质同理心低的个体表现出更强的西酞普兰对道德判断和行为的影响。综上所述，这些发现提供了独特的证据表明，血清素可以通过增强对伤害的厌恶来促进亲社会行为，而这种亲社会的情感会直接影响道德判断和道德行为。
