Hypothalamus volume and fatherhood: similarity across men and interindividual differences among dads

Most studies on mammalian caregiving and attachment have focused on the mother-child relationship, particularly in humans. Yet, recent re-considerations of attachment theory and changing societal roles of male caregivers have highlighted the necessity for research with fathers. In this pre-registered study (https://aspredicted.org/5uj5y.pdf), we examined the structure of the hypothalamus – an important subcortical brain area for caregiving and attachment behavior – in a sample of N=95 fathering (child age 5-6 years) and non-fathering men. To do so, we used a recently developed technique to accurately and efficiently identify the human hypothalamus in 3T MRI and calculate hypothalamus volume. Furthermore, we employed several self-report measures to assess interindividual differences in attachment style across all men, and caregiving specifically in fathers. While we found no difference in hypothalamus volume between fathers and non-fathers, fathers' interindividual variation in caregiving style was related to hypothalamus volume. Specifically, we observed that fathers who held greater belief in the importance of their role as a father and reported more enjoyment of interacting with their child had greater total hypothalamus volume. This finding suggests that there is interindividual variability in the association between brain structure and caregiving style in fathers, warranting further research.