To survive and protect: testosterone and the neuroendocrinology of human social behavior

The studies reported in this thesis show that despite the development that the human brain has undergone during evolution, this organ and the behavior it brings forth is still strongly sensitive to the effects of testosterone. Testosterone strengthens the neural response to sounds of crying babies, towards faces of anxious and untrustworthy individuals, and during the anticipation of reward. Testosterone further seems to reduce the communication between higher and lower brain structures. These important effects on the brain also manifests itself in behavior. Two studies described in this thesis show that testosterone reduces interpersonal trust and disrupts recognition of emotions of other individuals. An important aspect of these effects of testosterone on behavior is that they are strongly context-dependent and also to a large extent depend on individual differences, for example personality traits, or the amount of testosterone which one is exposed in the uterus. An overview of the literature also presented in this thesis shows that human social behavior is importantly affected by hormones such as testosterone and estradiol, and the neuropeptides oxytocin and vasopressin. As such, testosterone and vasopressin seem especially important in a socially challenging environment that requires action, while oxytocin and estradiol are more important for caring behaviors in a safe environment. The research in this thesis has a fundamental character, but in the long term may contribute to the development of treatment for clinical disorders such as social anxiety disorder.