Babies trigger 'dad brain' in new fathers

A new USC study of new fathers reveals that their brains undergo measurable changes after their babies arrive.

Some of those changes involve slight brain shrinkage. What's more, it appears that the brain’s changes in new fathers largely affects areas linked to empathy and visual processing. Such changes are believed to contribute to neuroplasticity — the brain’s ability to create and form new synaptic connections to adapt to new experiences.

"Becoming a parent entails changes to your lifestyle and your biology," said Darby Saxbe, the study's senior author who is a professor of psychology at USC Dornsife College of Letters, Arts and Sciences. "And it requires new skills like being able to empathize with a nonverbal infant, so it makes sense but has not been proven that the brain would be particularly plastic during the transition to parenthood as well."

The study appeared this month in the journal Cerebral Cortex. The work involved brain scans of 40 expectant fathers — 20 in the United States and 20 in Spain. For a comparison, the researchers also studied a group of 17 childless fathers that had been scanned in Spain.

A parenting brain network

In Spain, the researchers scanned the brains of the fathers (mean age of 35) before their partners became pregnant and then again two to three months after their partners gave birth. The childless men also underwent scans at similar intervals.

For the men in the U.S. study, researchers scanned their brains when their partners were in their third trimester (around 30 weeks along). They scanned the fathers’ brains again seven to nine months after the birth.

The scientists identified that the most significant changes, both in the Spanish and American men, occurred in the cortex — the brain's outer layer that is involved with attention, planning and executive functioning. Comparisons of the fathers' scans before the babies were born and afterward showed changes in portions of the cortex that have a role in processing visual information and in areas that are part of the brain's default mode network. The childless men had no such changes.

The default mode network may become active when someone is daydreaming, recalling a memory, or thinking about the future. Scientists believe the regions of this network are involved with empathy — thinking about other people's thoughts and feelings.

Dad brains vs. mom brains

Prior studies of mothers have shown changes in women's cortical areas that are key for the default mode network. The women also had changes in their subcortical areas (below the surface of the cortex) that are linked with emotion, threat and reward processing in mothers. This is the key difference between the mothers versus the fathers, the researchers said.

"It’s too soon to speculate with such a small sample but it might suggest that more, higher-order cognitive processing is involved in fatherhood specifically," Saxbe said, “whereas mothers are also showing change at the more basic mammalian level. In any case, the fact that we have found changes in the cortex both for fathers and mothers suggests that there is some remodeling of the social brain taking place."

Saxbe said she hopes to further study how the brain changes during fatherhood and examine their hormonal shifts.

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Other researchers involved in the study were Sofia Cardenas at USC Dornsife's Department of Psychology, plus a team in Spain from the Instituto de Investigación Sanitaria Gregorio Marañón in Madrid, the Centro de Investigación Biomédica en Red de Salud Mental at the Instituto de Salud Carlos II, Autonomous University of Barcelona and the Hospital del Mar Medical Research Institute, and from the Universidad Carlos III.

This work was supported by Ministerio de Ciencia, Instituto de Salud Carlos III, the European Regional Development Fund (ERDF), a predoctoral Fulbright grant to Cardenas was funded by a Miguel Servet Type II research contract, the “la Caixa” Foundation, the European Research Council and the Centro Nacional de Investigaciones Cardiovasculares.