The Surprising Way Men's Brains Change After They Become Parents

Dad jokes, dad bod, dad ... brain?

A new study adds to a growing body of evidence that birth mothers aren’t the only ones who undergo neurological developments after a child’s arrival. Dads’ brains change too — and it appears that these changes have an impact on their sleep and mental health.

Curtis Davis, a university professor, is the father of toddler twins who were born during the pandemic. He told HuffPost that the work of caring for them has been intense.

“[My wife and I] have careers, too, that could be demanding,” he said. “If there’s a gender norm or gender expectation, I kind of threw it out the window.”

When it comes to allocating the work of parenting, “it’s really about whoever gets to it,” Davis said. “If I recognize there’s something that needs to be handled, I just jump in.”

Davis does feel the weight of all this responsibility, both on his psyche and his sleep patterns. His job provides the children’s health coverage, and “there’s definitely some anxiety that comes with that,” he said.

He finds himself “being on pins and needles a little bit more,” he said. “The stress is definitely there.”

The highs of hands-on parenting, too, are significant. Davis and other dads reap great fulfillment from caring for their children.

It turns out, this caregiving actually alters dads’ brains

Darby Saxbe, a professor of psychology at the University of Southern California, has conducted multiple studies using MRI scans to measure changes in the brains of men who became fathers. Saxbe and her fellow researchers found that fathers lost brain volume — their brains grew smaller — after they became parents.

This shrinking of grey matter is similar to what other studies have found in women who became mothers, although the loss is less pronounced in fathers.

It’s important to note that a loss of brain volume, which sounds negative, doesn’t correspond with a loss of brain function, or of cognitive decline. It does mean that the brain has changed to adapt to a new situation: parenthood. Researchers have theorized that the loss of gray matter might represent a pruning of synapses, or connections in the brain, streamlining the way the brain works and making it more efficient.

In a subsequent study published in April 2024, Saxbe and her co-authors took images of 38 first-time dads’ brains while their partners were pregnant and when the babies were six months old. They also had the fathers answer questions about their involvement in parenting and their own well-being at three, six and twelve months after the child’s birth.

Again, they observed the loss of brain volume found in previous studies. Fathers lost an average of 1% of their gray matter after becoming parents.

As in similar studies conducted on mothers, Saxbe and her colleagues found that fathers who were more involved in child care showed greater brain changes. Dads who reported stronger bonding with the baby (either before or after birth), planned to take more time off from work, reported less parenting stress or spent more time with their babies experienced a larger loss in brain volume.

Not all of the changes associated with brain volume loss were positive, however. In that 2024 study, Saxbe found that fathers who lost more brain volume were also more likely to report signs of anxiety, depression, psychological distress and poor sleep. Because researchers found that the volume loss preceded these mental health and sleep problems, it appears that the brain changes cause the problems, not the other way around — although Saxbe cautioned reading too much into one study.

“This is preliminary research with small samples of parents,” Saxbe told HuffPost. “We really need to see more funding for studies of the parental brain so we can better understand plasticity during this critical and understudied life stage.”

Parenting changes fathers’ hormones, too

A loss in brain volume isn’t the only physiological change that dads who engage in caregiving undergo. The more parenting they do, the lower the levels of their testosterone dip. They also experience a rise in prolactin, a hormone involved in milk production, and in oxytocin, commonly known as the “love” or “connection” hormone. Oxytocin is what brings on labor, and is released when a person nurses a baby.

Gestational mothers, too, experience lower levels of testosterone and higher levels of oxytocin and prolactin, among other hormonal changes. These shifting hormones are widely viewed to be one of the reasons that people who give birth are at an increased risk for depression and anxiety.

Lee Gettler is a professor of anthropology at the University of Notre Dame who has published a number of studies about hormonal changes in fathers. He noted that while in most mammals, young are cared for primarily by the mother, there are plenty of other examples of fathers providing care in the animal kingdom, and they share a pattern of hormonal changes.

“In other vertebrates that have evolved invested fatherhood, males often
show declines in testosterone when they are cooperating with mothers to raise young,” Gettler told HuffPost.

In a large longitudinal study conducted in the Philippines, Gettler and other researchers studied the testosterone levels of men throughout their 20s, all of whom were single non-fathers when the study began.

“Men who became newly partnered new fathers experienced large biologically
meaningful declines in their testosterone, while testosterone was relatively stable in men who remained single non-fathers,” Gettler said.

Here, too, men who were more involved in parenting showed greater changes. “Fathers who spent the most time with their children and caring for them had lower testosterone than fathers who were not involved with care,” Gettler said.

Using data from this same study, researchers also found higher levels of prolactin — the hormone that spurs milk production — in fathers than non-fathers.

“Prolactin is commonly elevated in vertebrate fathers who help care for their young, suggesting it often helps support fathers’ care,” Gettler said.

In subsequent studies, Gettler found that fathers who had lower testosterone and higher levels of cortisol (a stress hormone) after their baby’s birth were more likely to be involved in caregiving tasks 2-4 months later.

“These findings also help show that dads’ biological responses to the transition to parenthood help prepare them for the demands of parenthood,” Gettler said.

Gettler and co-authors also found that fathers’ oxytocin rose after first holding their newborns. “First-time fathers show especially large increases in oxytocin,” Gettler said, showing that “the biology of new dads is ‘online’ and ready to help them engage and bond with their babies from the outset.”

Over time, Gettler and co-authors found, fathers who spent more time caregiving saw their testosterone levels continue to dip, while those who engaged less frequently in caregiving saw their testosterone levels rise again.

Taken together, all of these findings suggest a bidirectional relationship between fathers’ hormone levels and their caregiving. Greater changes in hormone levels predicted more involvement in caregiving, and more involvement in caregiving corresponded with greater hormonal shifts.

“Fathers have underlying physiology that can help support their engagement with their children from the beginning, and that can also respond to sensitive, nurturing father-child interactions,” Gettler said.

Both Saxbe and Gettler believe that their research highlights the importance of giving fathers — as well as other non-birthing parents — opportunities to engage in caretaking.

“This research highlights that anyone who devotes time to caring for a young child might show transformations in their brain or body. It helps underscore that great parents are ‘made, not born,’” Saxbe said.

Encouraging this caregiving and bonding can benefit the whole family. “These changes in fathers’ physiology can help encourage caregiving and
sensitivity, contributing to strong father-infant bonds and healthier family functioning,” Gettler said. “Paid leave for fathers when their babies are young can provide windows of time for these biological changes and positive interactions to come to their fullest expression.”

The mental health vulnerabilities that Saxbe found in her research are not a reason to discourage paternal caregiving, she said. Rather, they highlight the stress that caregiving involves and how all new parents are in need of support.

“It’s an important priority to support new parents’ well-being through policies that reduce stress and protect time in the first years after birth,” Saxbe said.

“Comprehensive paid family leave, with some time specifically earmarked for dads, is one important step in the right direction,” she continued, noting that countries with generous leave policies, like Finland, have found that fathers are more likely to take leave when it is specifically designated for them.

Tony Spatafora and his husband have “adopted and fostered many children over the past eight years” in their Los Angeles home. Spatafora told HuffPost, “I have matured in so many ways.”

These psychological changes are accompanied by anxiety at times, Spatafora said. “There are no handbooks ... the pressure from figuring out if you’re doing the right thing in the moment is tough.”

Spatafora works evenings as a bartender and his husband works during the day walking dogs. “Our schedules, and generous support network, allow us to be present for a lot of the time needed to care for our family,” Spatafora said.

“The ability to be in the moment, watching their development and sharing all that they suffer/savor is genius. We are blessed to have these small things that many miss.”