Serotonergic modulation of face-emotion recognition

Abstract

Facial expressions of basic emotions have been widely used to investigate the neural substrates of emotion processing, but little is known about the exact meaning of subjective changes provoked by perceiving facial expressions. Our assumption was that fearful faces would be related to the processing of potential threats, whereas angry faces would be related to the processing of proximal threats. Experimental studies have suggested that serotonin modulates the brain processes underlying defensive responses to environmental threats, facilitating risk assessment behavior elicited by potential threats and inhibiting fight or flight responses to proximal threats. In order to test these predictions about the relationship between fearful and angry faces and defensive behaviors, we carried out a review of the literature about the effects of pharmacological probes that affect 5-HTmediated neurotransmission on the perception of emotional faces. The hypothesis that angry faces would be processed as a proximal threat and that, as a consequence, their recognition would be impaired by an increase in 5-HT function was not supported by the results reviewed. In contrast, most of the studies that evaluated the behavioral effects of serotonin challenges showed that increased 5-HT neurotransmission facilitates the recognition of fearful faces, whereas its decrease impairs the same performance. These results agree with the hypothesis that fearful faces are processed as potential threats and that 5-HT enhances this brain processing.

Neuropsychological mechanism underlying antidepressant effect: a systematic meta-analysis

“…SSRIs and SNRIs are believed to block the reuptake and to potentiate neurotransmission of serotonin and noradrenaline, which are implicated in emotional processing. 4,41,57 Third, if antidepressants act to enhance 'topdown' regulation, we would expect this regulatory effect in healthy subjects as well, as altered emotional reactivity was observed in both samples. However, increased dlPFC activity caused by antidepressants was identified only in studies recruiting patients, but not in healthy volunteers studies.…”

“…Next, additional studies were collected by reviewing the reference list of relevant papers in the first step or through the 'related article' function of the PubMed database. Finally, the reference lists of several review articles 5,[40][41][42][43][44] were inspected for relevant studies.…”

“…Moreover, none of the existing reviews or meta-analyses systematically examined antidepressant effects on both positive and negative emotions. 5,[40][41][42][43][44] Among the relevant review and meta-analytic articles, only one study 43 conducted coordinate-based quantitative meta-analysis. However, this study was performed only across nine studies and did not consider the valence of emotional processes (that is, combined antidepressant effects on positive and negative emotions).…”

Physical versus Social Fear: A Fundamental Dichotomy

“…On the other hand, if angry expressions are perceived as a direct or proximal threat, detection of these expressions should be deteriorated. Taken together, studies (see Del-Ben, Ferreira, Alves-Neto, & Graeff, 2008) tend to show that an increase of serotoninergic neurotransmission improves fear recognition without deteriorating anger recognition. In other words, an angry facial expression identified in a member of the same species would not necessarily signal a direct threat, or would be not sufficient to be perceived as such.…”

Modulation of Emotional Faces Processing and Its Implication for Depression and Anxiety

“…Other emotions such as happiness and disgust, also seem to suffer interference in the serotonin levels for processing, though less consistent across studies. These studies (for review, see Del-Ben et al, 2008) have shown that decreased serotonin function through depletion of the supply of tryptophan in the diet reduced the recognition of facial expressions of fear in women, and in individuals of both sexes carrying the short allele of the serotonin transporter. On the other hand, the acute increase in the dietary intake of tryptophan increased the recognition of expressions of happiness and fear in female volunteers; supplementation of tryptophan for 14 days facilitated the identification of facial expressions of happiness and decreased the recognition of expressions of disgust in women but not in male subjects.…”