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Abstract
Serotonergic mechanisms mediate the expression of personality traits (such as impulsivity, aggression and anxiety) that are linked to vulnerability to psychological illnesses, and modulate the identification of emotional expressions in the face as well as learning about broader classes of appetitive and aversive signals. Faces with neutral expressions signal a variety of socially relevant information, such that inferences about the big five personality traits, including Neuroticism, Extraversion and Agreeableness, can be accurately made on the basis of emotionally neutral facial photographs. Given the close link between Neuroticism and psychological distress, we investigated the effects of diminished central serotonin activity (achieved by tryptophan depletion) upon the accuracy of 52 healthy (non-clinical) adults’ discriminations of personality from facial characteristics. All participants were able to discriminate reliably four of the big five traits. However, the tryptophan-depleted participants were specifically less accurate in discriminating Neuroticism than the matched non-depleted participants. These data suggest that central serotonin activity modulates the identification of not only negative facial emotional expression but also a broader class of signals about personality characteristics linked to psychological distress.
Highlights
Serotonin mechanisms mediate the expression of personality traits linked to mental illnesses (Takano et al 2007)
Fifty-two participants provide a statistical power of approximately 0.8 at α = .05 to detect medium effect sizes (0.5) in the one-sample t tests and medium-to-large effect sizes (0.7) in the two-sample tests. Since this is the first study of tryptophan depletion and the discrimination of personality traits from the face, we used a mixed-effects binomial model (Bates 2010) to test whether the inclusion of the above variables in the model moderated the reliability of treatment effects
An additional treatment × sex interaction term was not significant, β = 0.332, SE = 0.699, and did not improve the model, χ2(1) = 0.21. This is the first demonstration that serotonin function supports the perceptual discrimination of personality
Summary
Serotonin mechanisms mediate the expression of personality traits linked to mental illnesses (Takano et al 2007). Single doses of the selective serotonin reuptake inhibitor (SSRI), citalopram, improve fear recognition in healthy adults (Browning et al 2007) and normalize recognition of fearful (and positive) facial expressions in previously depressed individuals (Bhagwagar et al 2004). These effects are likely to be mediated by altered signaling within neural circuitry encompassing the amygdala (Harmer et al 2004), suggesting that anti-depressant modulation of monoaminergic activity within limbic circuits alters sensitivity to facial emotional signals (as well as broader cognitive biases) to support delayed therapeutic effects (Anderson et al 2011; Booij and Van der Does 2011; Hayward et al 2005; Harmer et al 2006; Walsh and Harmer 2015). We tested the specific prediction that tryptophan depletion impairs accurate identification of Neuroticism from neutral facial expressions in healthy adult volunteers
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