The psychobiology of early fatherhood: exploring the neural and hormonal aspects

Fathers’ involvement and parenting behaviors are associated with positive child development, attachment security, and well-being of the child. Interestingly, only little research focused on the onset of these parental behaviors and its possible underlying biological mechanism in men becoming a father. The overall aim of the current dissertation was to further explore the psychobiology of fatherhood and to test the associations between the neural and hormonal components and parenting behavior in fathers. In Chapter 2, we reviewed previous literature on fatherhood and proposed a biobehavioral model of the emergence of fatherhood incorporating social-cultural, behavioral, hormonal, and neural aspects in the context of the prenatal, perinatal and postnatal phases of fatherhood. In Chapter 3, we focused on the influence of vasopressin administration and infant’s birth on fathers’ thoughts and feelings about their infant and the desired relationship measured via the Five Minute Speech Sample. Analyses did not reveal a significant effect of vasopressin administration on FMSS-based expressed emotion, emotional content, and emotional prosody in the current study. These results suggest that fathers’ thoughts and feelings about their unborn child might be independent of vasopressin. In the context of infant’s birth, analyses showed that the fathers stated more positive comments about their infant after birth compared to when they were expecting. Moreover, a decrease in emotional prosody parameters was observed. Based on these results, it might be speculated that infant’s birth is more influential with regard to fathers’ expressed thoughts and feelings than vasopressin administration in the late prenatal phase of fatherhood. In Chapter 4, we studied the relation between oxytocin, vasopressin, testosterone and cortisol, and fathers’ sensitive parenting behavior in the early postnatal phase of fatherhood. Structural Equation Models did not reveal any significant associations between paternal sensitivity and basal hormone levels or hormone reactivity. Exploration of interaction effects of basal hormones on sensitivity indicated that the interaction testosterone*cortisol best predicted paternal sensitivity. Post-hoc analyses indicated a stronger positive association between testosterone and sensitivity for fathers with lower cortisol levels compared to fathers with higher cortisol levels. These results suggest that observed variation in paternal sensitivity might be better explained by interactions between hormones than by single hormone levels. In Chapter 5, we explored fathers’ protective parenting behavior and its possible hormonal and neural correlates. Analyses revealed that the paradigms for self-reported and observed protective behavior obtained good reliability. However, there was little overlap between observed and self-reported protective behavior. FMRI analyses revealed that we replicated and validated the role of several brain networks in the processing of infant-threatening situations previously observed by van ‘t Veer and colleagues (2019). Lastly, bivariate correlations revealed no associations between basal testosterone and vasopressin, neural responses and paternal protective behavior. Based on these findings, it may be concluded that both testosterone and vasopressin baseline levels and neural responses to infant threatening situations may not be suitable correlates of paternal protective behavior in the early phase of fatherhood. In sum, based on the empirical results presented in this dissertation, we cannot conclude that basal hormone levels and hormone reactivity are related to fathers’ sensitive and protective behavior in the late prenatal and early postnatal phase of fatherhood. Moreover, our results do not support our hypothesis that neural responses to infant threatening stimuli are related to behavioral components of infant protection in fathers. Interestingly, exploratory analyses indicated that the interaction effects of basal hormones may be promising for future research to explain observed variations in paternal behavior. Further examination of the psychobiology of paternal behavior is necessary to better understand the role of the neuroendocrine system in the development of paternal protection and paternal sensitivity.