Serotonin depletion amplifies distinct human social emotions as a function of individual differences in personality

Abstract

Serotonin is involved in a wide range of mental capacities essential for navigating the social world, including emotion and impulse control. Much recent work on serotonin and social functioning has focused on decision-making. Here we investigated the influence of serotonin on human emotional reactions to social conflict. We used a novel computerised task that required mentally simulating social situations involving unjust harm and found that depleting the serotonin precursor tryptophan-in a double-blind randomised placebo-controlled design-enhanced emotional responses to the scenarios in a large sample of healthy volunteers (n = 73), and interacted with individual differences in trait personality to produce distinctive human emotions. Whereas guilt was preferentially elevated in highly empathic participants, annoyance was potentiated in those high in trait psychopathy, with medium to large effect sizes. Our findings show how individual differences in personality, when combined with fluctuations of serotonin, may produce diverse emotional phenotypes. This has implications for understanding vulnerability to psychopathology, determining who may be more sensitive to serotonin-modulating treatments, and casts new light on the functions of serotonin in emotional processing.

Fig. 1. Moral emotions task schematic.

Three example slides of a trial are shown. Feeling “bad” was assessed with a rating scale on a fourth slide.

Fig. 2. Effects of trait empathy on how serotonin depletion influences emotion.

Shading indicates 1 standard error. Each point represents the average emotion ratings for each individual, collapsed across agency and intentionality. a The highly empathic reported more guilt following depletion relative to when on placebo. b Shame was significantly elevated in individuals high in trait empathy on both placebo and depletion.

Fig. 3. Effects of trait psychopathy and impulsivity on emotional effects of serotonin depletion.

Shading indicates 1 standard error. Each point represents the average emotion ratings for each individual, collapsed across agency and intentionality. a Annoyance was potentiated by serotonin depletion in high-trait psychopathy. b Trait impulsivity did not significantly enhance the effects of ATD on annoyance.

Fig. 4. Blood analysis results.

Error bars represent 1 standard error. Significance at p < 5 ×10⁻²⁷ is denoted by #####. n.s. denotes not significant.