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Neuroimaging study finds reductions in gray matter in first-time fathers


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

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

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

The researchers observed changes in the cortex – the outer layer of the brain involved in attention, planning and executive functioning – in the fathers. But no significant changes were detected in the control group.

In the fathers, the researchers found reductions in cortical volume in the visual system and the default mode network, which is believed 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.

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

“Becoming a parent involves changes in your lifestyle and biology,” co-author Darby Saxbe added in a press release. “And that requires new skills like being able to empathize with a non-verbal baby, so that makes sense but it hasn’t been proven that the brain would also be particularly plastic during the transition to parenthood.”

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

“The main challenge of this study is that we analyzed two different samples of fathers, one acquired in Spain and the other in California,” explained Martínez-García. “The two samples differed in MRI device and time points. But we minimized this issue by calculating the longitudinal brain change and controlling for the elapsed time between the two MRI sessions. The two samples also did not collected the same information regarding the father-child relationship, which complicates the inclusion of these variables in the analysis.

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

But there seem to be differences between mothers and fathers. Previous research has revealed changes in the subcortical areas of the mother, the area below the surface of the cortex, particularly in regions associated with the processing of emotions, threats and rewards.

“Mothers who undergo pregnancy and parents who don’t 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 huge amount of hormonal exposure at this time). Structural brain changes in first-time fathers occur specifically in cortical regions, not in subcortical regions (whereas biological mothers show widespread changes) Cortical regions are more involved in social cognition, goal-directed attention, and empathy, while subcortical regions control a ancient reward-motivation circuitry, both of which are essential for optimal parenting.

“It’s too early to speculate with such a small sample, but it might suggest that more higher-order cognitive processes are specifically involved in fatherhood,” Saxbe said, “as mothers also show higher-level changes. In any case, the fact that we found changes in the cortex for both fathers and mothers suggests that there is some social brain remodeling going on.

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

The study, “First-time fathers show longitudinal reductions in cortical gray matter volume: 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. Saxbé.