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Attachment is the inborn bias of human children to seek the availability of familiar caregivers in times of stress. It has been observed from ancient times and in many cultures, and scaffolds further physical, cognitive, and socioemotional development. The security of these relationships is shaped by the continuity and quality of the child-rearing environment, and is independent of biological ties to the caregiver. In this chapter, the child’s right to a “good-enough”—that is, at least minimally adequate but not necessarily ‘best’--family life and the importance of a stable network of attachment relationships is highlighted. Legal issues raised by multi-parent care, including questions around the use of attachment-based assessments for custody decisions, are addressed. Attachment theory is well equipped to inform what caregiving arrangements children need, and legislators, judges, and lawyers may consult it as a source of insight into “good-enough” care arrangements in the interest of the child.

The aim of the current dissertation was to shed light on various dimensions of fatherhood. In the study presented in Chapter 2, we investigated developmental trajectories of infant sleep from 3 to 24 months old, and we examined associations with infant-parent attachment security and dependency. We found no associations between the duration and frequency of infant nighttime awakenings and the infant’s dependency level toward the parents. Surprisingly, we found that a longer duration and a higher frequency of infant nighttime awakenings was associated with higher infant-father attachment security. Moreover, we reported that a longer duration of infant nighttime awakenings was associated with lower infant-mother attachment security. In our post-hoc analyses, we examined whether the negative association between infant sleep problems and infant-father attachment security could be explained by an increase in paternal involvement at night, however, we found no evidence for this explanation. In the study presented in Chapter 3, we examined whether prenatal family alliance and prenatal paternal testosterone levels predicted infant–mother and infant–father attachment security and whether this association was mediated by postnatal family alliance and postnatal paternal testosterone levels. Our findings showed that a more positive prenatal family alliance predicted higher infant–father attachment security but not infant–mother attachment security. Importantly, as family alliance can be observed prior to the birth of the baby, interventions to improve family alliance can be implemented prior to the birth of the baby. Paternal testosterone levels did not mediate the relation between prenatal family alliance and infant-mother and infant-father attachment security. In Chapter 4, we presented a study protocol of a randomized, double-blind, placebo-controlled within-subject experiment to investigate the effects of intranasal administration of oxytocin and vasopressin on fathers’ neural and behavioral responses to infant cry sounds and infant threat. The study protocol provides a rationale for conducting experiments with oxytocin and vasopressin administration in first-time fathers in the early phase of parenthood. In Chapter 5, we presented a randomized double-blind placebo-controlled within-subject study to examine the effects of oxytocin and vasopressin administration on fathers’ sensitive and challenging parenting behaviors (CPB). Our results showed that fathers who reported higher levels of experienced parental love withdrawal were less sensitive in the oxytocin condition as compared to the placebo condition, whereas fathers with lower levels of experienced parental love withdrawal showed similar levels of paternal sensitivity in the oxytocin and placebo condition. These findings indicate that oxytocin administration can reduce sensitive caregiving, depending on fathers’ own childhood experiences. We reported no effects of vasopressin administration on paternal sensitivity, neither did oxytocin or vasopressin administration affect fathers’ CPB. In Chapter 6, we conducted a randomized double-blind placebo-controlled within-subject study to examine the effects of oxytocin and vasopressin administration on fathers’ neural responses to infant cry sounds. Region of interest analyses showed that oxytocin and vasopressin administration decreased fathers’ amygdala activation in response to infant cry sounds. Reduced amygdala activation after oxytocin administration may point to decreased feelings of anxiety or aversion towards the crying infant. Albeit speculatively, reduced amygdala activation after vasopressin administration might be explained by contextual factors (e.g., absence of high levels of threat, unfamiliarity of the infant) or might point to an affiliative reaction to infant crying. To conclude, findings presented in the current dissertation underscore the importance of including both mothers and fathers in attachment research in order to gain a better understanding of how parenting behaviors contribute to the development of the attachment relationship with each parent. Moreover, unravelling how hormonal, neural and behavioral responses (bi-directionally) interact with each other remains an important challenge for future studies.

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.

Summary Even though the relatively limited available scientific literature indicates that fathers are important for child development from the earliest stages of parenthood onward, parenting research still predominantly focusses on mothers only. In this thesis, we report on findings resulting from a series of randomized controlled trials investigating neurobiological parameters across men’s transition into parenthood; the Father Trials. In Chapter 2, we report that fathers’ behavioural responses to infant crying, as well as baseline testosterone, are stable across the perinatal period. In contrast, fathers’ neural response to infant crying was found to undergo a noteworthy change from the prenatal to the postnatal period, indicating that some neural response to infant crying (e.g., those involved in visual imagery) emerge after the birth of their child. We also found that postnatal neural activation in response to infant crying in the right precentral gyrus was strongly related to postnatal parenting sensitivity, possibly indicating an important association between neural reactivity in response to infant signals and parenting quality. In Chapter 3 we report that fathers’ experiences of childhood maltreatment were found to be associated with inadequate inhibitory control over behavioural responses and / or emotional hyperreactivity in response to infant crying in the perinatal period. Specifically, this effect was only present for fathers with low structural connectivity between the prefrontal cortex and the amygdala (i.e., uncinate fasciculus). These findings suggest that fathers are more or less resilient to the detrimental behavioural correlates of negative caregiving experiences dependening upon their brain’s white matter structure. In Chapter 4 we report on the behavioural effects of arginine vasopressin (AVP); a hormone which has been proposed to play a vital role in fatherhood. AVP administration in expectant fathers was found to lead to inadequate inhibitory control over behavioural responses and / or emotional hyperreactivity while viewing an unknown infant image compared to viewing an image representing fathers’ own infant, while the opposite was true under placebo. These findings suggest that AVP may be involved in the evolutionary selected ability to detect kinship and possibly induces an increase in protective aggression based on preference for facial resemblance in offspring. In Chapter 5 we report on the development and feasibility of the Prenatal Video-feedback Intervention to promote Positive Parenting (VIPP-PRE), aimed at improving postnatal parenting quality and stimulating involvement in first-time fathers. With the use of real-time ultrasound images, expectant fathers interacted with their unborn children and were given feedback aimed at improving their ability to detect and understand their child’s behavioural signals as well as reinforcing fathers’ timely sensitive responses to those signals. Based on the evaluation by participating fathers and sonographers, we concluded that the VIPP-PRE is feasible and is received positively. Moreover, we found that fathers receiving the VIPP-PRE, compared to those receiving a control intervention, reported to have gained more insight into their relationship with their child, a better understanding of their child and its feelings, and more insight into their communication with their child. In conclusion, we have found support for the claim that several neurobiological processes (i.e., neural reactivity to infant signals and the vasopressin system) play a role in preparing expectant fathers for parenthood. However, fathers’ quality of care is associated with their own childhood experiences, depending upon fathers’ brain architecture. Although there has been a sharp increase in studies examining paternal behaviour and its underlying mechanisms, there is still much unknown. Within the Father Trials project, we aimed to put fathers at the heart of studying parenting and have provided an evidence-based, prenatal, and interaction-focused intervention aimed at providing support during the transition into fatherhood.

Summary Neural face processing Our mediation hypothesis that intervention effects on maternal sensitivity would be induced by changes in neural face processing was not supported. Although we found more efficient neural face processing after the intervention (Chapter 3), that change did not promote maternal sensitivity as VIPP-SD effects on a behavioral level were absent in our study (Chapter 4). These findings ask for careful reflection. Our findings showed a significant decrease in N170 amplitudes, a component reflecting the relatively early stage of encoding and processing faces in the intervention group compared to the control group. This finding indicated that the intervention resulted in less effortful, more efficient neural face processing. Although stronger N170 amplitudes have been related to more extensive information processing, reductions in neural activity during information processing may reflect neural efficiency. To illustrate, inverted faces elicit stronger N170 responses, which reflects the additional neural effort required to process this type of faces. Less effortful information processing, due to practice for instance, has been associated with a reduction in neural effort required to processes information. In the context of the VIPP-SD program, the intervention themes related to maternal sensitivity focus on accurate perception and interpretation of children’s displays of emotions, for which faces are a central communication channel. As such, training mothers’ observational skills might have improved their ability to scan their children’s faces for emotional cues and reduced the neural effort needed to process child faces. This interpretation would be consistent with the reduced N170 amplitudes that we observed. However, the results of the mediation analyses presented in Chapter 4 showed that the VIPP-SD program did not significantly enhance observed maternal sensitivity in our sample, and neural face processing was not involved as mediator. A possible explanation for this pattern of results might be found in the time-window between assessments. On average, there was a three-week period between our EEG measure and the maternal sensitivity assessments. That was perhaps too short for neural effects to translate into observable changes in maternal sensitivity. Inhibitory control We did not obtain evidence for our mediation hypothesis that intervention effects on sensitive discipline would be induced through improved inhibitory control. We found an intervention effect on inhibitory control, however opposite to our expectations, as inhibitory control improved in the control group whereas the intervention group did not significantly change over time. This finding could indicate a ‘normative’ time/practice-related improvement in the control group, something that is typically observed when participants perform the stop signal task more than once. Speculatively, that this normative improvement was interrupted in the intervention group, possibly due to VIPP-SD induced restructuring of parenting schemas. That is, the sensitive discipline themes of the intervention confront mothers with their own and their children’s behavior, which appeals to reinterpretation and reevaluation of the mothers’ behavioral repertoire. Restructuring parenting schemas requires cognitive effort. Such complex cognitive changes may have come at the cost of other cognitive operations, such as inhibitory control, that we observed at the time of our assessment. The mediation analysis showed that inhibitory control was unrelated to sensitive discipline and there was no evidence for the expected increase in observed sensitive discipline in the intervention group. Again, the time-window between assessments might explain the results. If the intervention indeed triggered reorganization of previously established parenting schemas, consolidation into stable updated parenting schemas that are accessible during the assessment of disciplining might take more time than the lag between our assessments. We speculate that parenting schemas of discipline strategies might have been ‘under reconstruction’ during our assessment of sensitive discipline, which could have diminished positive effects on a behavioral level.