Neuroimaging study finds gray matter reductions in first-time fathers

New neuroscience research provides evidence that becoming a father results in brain structure alterations. The findings, published in Cerebral Cortex, indicate that men who become fathers tend to experience changes in cortical regions associated with social interaction and visual processing.

“My main focus is to disentangle the adaptations of the human maternal brain through pregnancy and postpartum,” said study author Magdalena Martínez-García, a member of the Neuromaternal group at the Instituto de Investigación Sanitaria Gregorio Marañón of Madrid. “But, as part of that research, we need to rule out the amount of brain plasticity triggered by factors outside the reproductive experience, such as the interaction with the baby, among other factors. In this sense, studying fathers offers a unique opportunity to study experience-induced brain plasticity.”

For the new study, Martínez-García and her colleagues examined structural neuroimaging data in 40 expectant fathers before and after the birth of their first child. They also examined a control group of 17 childless men.

The researchers observed changes in the cortex — the brain’s outer layer that is involved with attention, planning and executive functioning — among the fathers. But no significant changes were detected in the control group.

Among fathers, the researchers found cortical volume reductions within the visual system and the default mode network, which is thought to be involved in self-referential thoughts, such as planning for the future or reflecting on the past. Research has shown that the default mode network is also active when people are thinking about others, such as during social cognition tasks. Changes in the network “may support parents’ ability to mentalize with their infants,” the researchers said.

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“The brains of parents are shaped by both pregnancy factors and experience factors during the postpartum,” Martínez-García told PsyPost.

“Becoming a parent entails changes to your lifestyle and your biology,” added co-author Darby Saxbe in a news release. “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.”

Twenty fathers were from Spain, while the other 20 were from the United States. In Spain, the fathers underwent brain scans before their partners became pregnant and then again two to three months after their partners gave birth. For the men in the U.S. study, researchers scanned the father’s brains when their partners were in their third trimester and then scanned their brains again seven to nine months after the birth.

“The main challenge of this study is that we analyzed two different samples of fathers, one acquired in Spain and the other one in California,” Martínez-García explained. “The two samples differed in the MRI machine and time points. But we minimized this problem by calculating the longitudinal brain change, and controlling for the time spanned between the two MRI sessions. The two samples also didn’t collect the same information regarding the father-infant relationship, difficulting the inclusion of these variables in the analysis.”

“We were initially expecting more differences between the Spanish and Californian samples,” she added. “It surprised us how similar the pattern of brain changes was, stressing that, despite cultural and political differences between the countries, brain changes during parenthood share core components.”

But there do appear to be some differences between mothers and fathers. Previous research has uncovered changes in mother’s subcortical areas, the area below the surface of the cortex, particularly in regions associated with emotion, threat and reward processing.

“Both mothers that undergo pregnancy and parents who do not will experience some degree of brain plasticity during the transition to parenthood,” Martínez-García told PsyPost. “But pregnancy factors trigger more pronounced changes (due to the enormous amount of hormonal exposure at this time). The structural brain changes in first-time fathers occur specifically in cortical regions, and not in subcortical regions (while biological mothers display widespread changes). Cortical regions are more involved in social cognition, goal-directed attention, and empathy, while subcortical regions control an ancient reward-motivation circuit, both of which are key for optimal parenting.”

“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.”

“This study was a collaboration between the Neuromaternal group in Madrid (led by Susana Carmona), and the NEST lab of the University of Southern California in Los Angeles (led by Darby Saxbe),” Martínez-García noted.

The study, “First-time fathers show longitudinal gray matter cortical volume reductions: evidence from two international samples“, was authored by Magdalena Martínez-García, María Paternina-Die, Sofia I Cardenas, Oscar Vilarroya, Manuel Desco, Susanna Carmona, and Darby E. Saxbe.