Although animal researchers established the role of testosterone as a 'social hormone' decades ago, the investigation of its causal influence on human social behaviors has only recently begun. Here, we review and discuss recent studies showing the causal effects of testosterone on social interactions in animals and humans, and outline the basic neurobiological mechanisms that might underlie these effects. Based on these recent findings, we argue that the role of testosterone in human social behavior might be best understood in terms of the search for, and maintenance of, social status. Testosterone in contextTestosterone is one of the major sex hormones produced by the body, occurring in both men and women. In men, it is mainly produced by the Leydig cells of the testes, whereas the ovaries and placenta produce it in women. The adrenal cortex also secretes it in both sexes [1]. Testosterone has a well-known and important role in the development of secondary sexual attributes; for example, increased muscle, bone mass and body hair in men. However, it is also of special interest in the study of socio-emotional and economic behavior because it influences the brain in archetypical situations, such as fight, flight, mating and the search and struggle for status [2].Three recent developments argue for a causal role of testosterone as a 'social' hormone. First, recent years have seen the advent of acute single-dose testosterone administration studies in humans. This methodological innovation is important because it enables the study of the effect of testosterone on complex social interactions between human subjects, rather than its impact on the more difficult to interpret behavioral repertoire of non-human animals. Moreover, testosterone administration studies can establish the causality of testosterone in facilitating particular motives and behaviors.Second, the advent of sophisticated behavioral paradigms allows for the study of social emotional processes, such as threat vigilance, and affiliative behaviors, such as facial mimicry, emotion inference and trust. These paradigms not only make it possible to assess whether the hormone plays a role in modulating behavior, but also add to the understanding of the motives that might underlie human interactions. Third, the integration of experimental economic paradigms into the study of hormonal effects on behavior provides an opportunity to identify the precise channels through which testosterone affects social interaction in a controlled laboratory environment.Together, these advances offer an exciting new opportunity to reassess the role of testosterone in driving behavior. Here, we summarize recent evidence using these approaches and argue that the role of testosterone in social interaction in humans might be best conceptualized as bringing motives for seeking social status to the fore. We also discuss the psychological and neurobiological channels that might underlie these effects.Animal models of the role of testosterone in social interactions Early evidence for the r...

3,4-Methylenedioxymethamphetamine (MDMA, 'ecstasy') releases serotonin and norepinephrine. MDMA is reported to produce empathogenic and prosocial feelings. It is unknown whether MDMA in fact alters empathic concern and prosocial behavior. We investigated the acute effects of MDMA using the Multifaceted Empathy Test (MET), dynamic Face Emotion Recognition Task (FERT) and Social Value Orientation (SVO) test. We also assessed effects of MDMA on plasma levels of hormones involved in social behavior using a placebo-controlled, double-blind, random-order, cross-over design in 32 healthy volunteers (16 women). MDMA enhanced explicit and implicit emotional empathy in the MET and increased prosocial behavior in the SVO test in men. MDMA did not alter cognitive empathy in the MET but impaired the identification of negative emotions, including fearful, angry and sad faces, in the FERT, particularly in women. MDMA increased plasma levels of cortisol and prolactin, which are markers of serotonergic and noradrenergic activity, and of oxytocin, which has been associated with prosocial behavior. In summary, MDMA sex-specifically altered the recognition of emotions, emotional empathy and prosociality. These effects likely enhance sociability when MDMA is used recreationally and may be useful when MDMA is administered in conjunction with psychotherapy in patients with social dysfunction or post-traumatic stress disorder.

Both biosociological and psychological models, as well as animal research, suggest that testosterone has a key role in social interactions. Evidence from animal studies in rodents shows that testosterone causes aggressive behaviour towards conspecifics. Folk wisdom generalizes and adapts these findings to humans, suggesting that testosterone induces antisocial, egoistic, or even aggressive human behaviours. However, many researchers have questioned this folk hypothesis, arguing that testosterone is primarily involved in status-related behaviours in challenging social interactions, but causal evidence that discriminates between these views is sparse. Here we show that the sublingual administration of a single dose of testosterone in women causes a substantial increase in fair bargaining behaviour, thereby reducing bargaining conflicts and increasing the efficiency of social interactions. However, subjects who believed that they received testosterone-regardless of whether they actually received it or not-behaved much more unfairly than those who believed that they were treated with placebo. Thus, the folk hypothesis seems to generate a strong negative association between subjects' beliefs and the fairness of their offers, even though testosterone administration actually causes a substantial increase in the frequency of fair bargaining offers in our experiment.

Humans are noted for their capacity to over-ride self-interest in favor of normatively valued goals. We examined the neural circuitry that is causally involved in normative, fairness-related decisions by generating a temporarily diminished capacity for costly normative behavior, a 'deviant' case, through non-invasive brain stimulation (repetitive transcranial magnetic stimulation) and compared normal subjects' functional magnetic resonance imaging signals with those of the deviant subjects. When fairness and economic self-interest were in conflict, normal subjects (who make costly normative decisions at a much higher frequency) displayed significantly higher activity in, and connectivity between, the right dorsolateral prefrontal cortex (DLPFC) and the posterior ventromedial prefrontal cortex (pVMPFC). In contrast, when there was no conflict between fairness and economic self-interest, both types of subjects displayed identical neural patterns and behaved identically. These findings suggest that a parsimonious prefrontal network, the activation of right DLPFC and pVMPFC, and the connectivity between them, facilitates subjects' willingness to incur the cost of normative decisions.