A Systematic Review of the Role of Oxytocin, Cortisol, and Testosterone in Facial Emotional Processing

SIMPLE SUMMARY: The scientific community has paid special attention to facial emotional expression due to its importance in human surveillance as a communication tool. Humans need decoding abilities to understand the meaning of facial expressions and act accordingly. This ability is partly regulated by biochemical signals such as hormones, and it is of growing interest in understanding the role played by specific hormones such as oxytocin, cortisol, and testosterone. To date, there is a gap in the scientific literature summarizing how the manipulation of endogenous levels of oxytocin, cortisol, and testosterone through the exogenous administration of these hormones affects the processing of facial emotional expressions during adulthood in healthy and clinical populations of both genders. Therefore, we conducted a systematic review to summarize the evidence about how these three hormones influence facial emotional processing, paying special attention to studies that employed robust research designs (e.g., randomized, single- or double-blind, and/or placebo-controlled). The results obtained did not present a consistent pattern of association between the variables. In any case, these hormones slightly influenced facial emotion processing, but it is obviously extremely difficult to establish a direct association. To correctly understand the hormones’ influence, it is necessary to consider other factors such as the emotional valence and the participants’ gender, among others, which played an important role. ABSTRACT: A topic of interest is the way decoding and interpreting facial emotional expressions can lead to mutual understanding. Facial emotional expression is a basic source of information that guarantees the functioning of other higher cognitive processes (e.g., empathy, cooperativity, prosociality, or decision-making, among others). In this regard, hormones such as oxytocin, cortisol, and/or testosterone have been found to be important in modifying facial emotion processing. In fact, brain structures that participate in facial emotion processing have been shown to be rich in receptors for these hormones. Nonetheless, much of this research has been based on correlational designs. In recent years, a growing number of researchers have tried to carry out controlled laboratory manipulation of these hormones by administering synthetic forms of these hormones. The main objective of this study was to carry out a systematic review of studies that assess whether manipulation of these three hormones effectively promotes significant alterations in facial emotional processing. To carry out this review, PRISMA quality criteria for reviews were followed, using the following digital databases: PsycINFO, PubMed, Dialnet, Psicodoc, Web of Knowledge, and the Cochrane Library, and focusing on manuscripts with a robust research design (e.g., randomized, single- or double-blind, and/or placebo-controlled) to increase the value of this systematic review. An initial identification of 6340 abstracts and retrieval of 910 full texts led to the final inclusion of 101 papers that met all the inclusion criteria. Only about 18% of the manuscripts included reported a direct effect of hormone manipulation. In fact, emotional accuracy seemed to be enhanced after oxytocin increases, but it diminished when cortisol and/or testosterone increased. Nonetheless, when emotional valence and participants’ gender were included, hormonal manipulation reached significance (in around 53% of the articles). In fact, these studies offered a heterogeneous pattern in the way these hormones altered speed processing, attention, and memory. This study reinforces the idea that these hormones are important, but not the main modulators of facial emotion processing. As our comprehension of hormonal effects on emotional processing improves, the potential to design good treatments to improve this ability will be greater.