Becoming a father can shrink your brain, new study says

Too many diaper changes. Too little sleep. As if taking care of a newborn wasn’t overwhelming enough, a recent study has found that men’s brains shrink after the birth of their first child. Instead of a sign of things gone wrong, scientists think that these changes are an important step in becoming a good parent. 

A similar shrinking effect has been seen before in new mothers, but the new study is one of the first clear indications that this phenomenon exists in fathers too, though more subtly. It implies that physiological change can occur even in parents who don’t undergo the transformative experience of pregnancy.

Fathers shouldn’t freak out over these findings, as “change can be a good thing,” says Darby Saxbe, the senior author of the study. She is a University of Southern California psychologist who studies how the transition into parenthood affects the brain.

The positive change she’s referring to is neuroplasticity, the brain’s ability to remodel itself as circumstances change. Throughout our lives, our brains prune synapses we no longer use to make space for new growth. It happens when we learn language as babies, when we emotionally mature in adolescence, and when we learn new skills as adults.

The recent study suggests that becoming a parent for the first time is another period of neuroplasticity. “Infants require constant care, so it makes a lot of sense that the brain would need to remodel to reflect that,” says Saxbe. Pruning allows the brain to take in new information and adapt to new conditions.

The effect in fathers is subtle, including a reduction of about one percent in the brain’s cortical regions. This is notably seen in the visual and default mode networks, areas of the brain involved with attention and empathy. This may help dads recognize and anticipate the baby’s needs, explains lead author Magdalena Martinez-Garcia, a neuroscience PhD student at the Instituto de Investigación Sanitaria Gregorio Marañón in Madrid. The study’s conclusions were based on magnetic resonance images (MRIs) of the brains of 40 first-time fathers. Out of the 40 fathers, 20 were from Barcelona and 20 were from Los Angeles.

Despite the study’s small size and subtle results, an expert who was uninvolved in the research is excited about its findings. 

“It indirectly provides evidence that these types of brain changes might occur for people who don’t directly experience pregnancy,” says Pilyoung Kim, a psychologist at the University of Denver who investigates brain development in mothers and fathers.

In pregnant women, striking and widespread brain shrinkages have been documented by previous studies. These neurological changes are thought to be influenced by hormones and help mothers strengthen emotional bonds with their babies. But the new study indicates that at least some of the changes could come from the experience of being a new parent.

In fathers, the brain changes are not only more minute. They also vary more widely between participants. The study authors think this may be due to individual variations in parenting involvement, or differences in cultural contexts or paternal leave policies. But these theories are still highly speculative, as the study was too small to draw stronger conclusions.

Parsing out how these cultural factors interact is the next step to furthering our knowledge of how our brains respond to parenthood, experts say.

“Everything that we do is mediated through the brain, so I think understanding the brain is critical to understanding the experience the parents have during this period of time,” says Kim. Studying these transformations and experiences can inform how we shape policies like family leave to support parents and their infants through this life transition, adds California’s Saxbe.

These new findings show that dads and their brains are a part of the equation that shouldn’t be overlooked. “Now that we’re finding evidence of change,” says Saxbe, “it’s really exciting to try to understand more about why.”