Changes in left hippocampal volume in first-time fathers: Associations with oxytocin, testosterone, and adaptation to parenthood.

The parenting brain may undergo remodeling that supports the adjustment to new parenthood. Prior work on human mothers has found gray matter volume decreases from preconception to early postpartum in multiple structures, including the left hippocampus, which was the only structure to show gray matter volume recovery at 2 years postpartum. This is consistent with evidence from animal models that the hippocampus is unusually plastic across reproductive transitions. However, no studies have focused specifically on hippocampal volume changes in human fathers. Among 38 men who were scanned by magnetic resonance imaging (MRI) before and after having their first child, individual differences in left hippocampal volume changes were associated with men's prenatal oxytocin, postpartum testosterone, and postpartum adaptation to parenthood. Across the whole sample, hippocampal volumes did not change significantly from prenatal to postpartum. However, men who showed larger increases in left hippocampal volume from prenatal to postpartum reported stronger parent-child bonding and affectionate attachment and lower parenting stress. Fathers with higher levels of prenatal oxytocin showed larger left hippocampal volume increases across the transition to parenthood. In turn, greater increases in left hippocampal volume predicted lower postpartum testosterone after adjusting for prenatal testosterone. These findings did not extend to the right hippocampus. In conclusion, remodeling of the left hippocampus across the transition to new fatherhood may reflect adaptation to parenthood in human males.