When our daughter was born this year, our lives changed forever.
For my wife and me, there was a clear event horizon boundary separating a Before and an After – a reality that has been etched in our brains and biology.
Research shows that mothers undergo dramatic changes during pregnancy and following childbirth akin to a “second puberty,” which causes hormonal fluctuations and a shrinking brain (which sounds bad but is more like streamlining neural connections in a positive way).
Recent studies suggest that, like mothers, fathers may undergo a profound shift in their biology and brains in preparation for and response to the responsibilities of parenthood.
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These biological changes may actually be adaptive to the challenges of parenthood for any parent, research suggests. And there is even evidence that parenthood is beneficial and neuroprotective for the brain, even if the stresses of 4 a.m. feedings and inconsolable crying may not feel like it at the time.
This research is “a very important signal for us as scientists, as a society, that caregiving is just a universal thing and it just changes you forever probably,” said Negin Daneshnia, a psychologist at RWTH Aachen University in Germany.
What dad brain looks like
Becoming a father (and, presumably, any parent who hasn’t given birth) sculpts the brain – how it looks, how it is connected and how it functions.
The largest changes are in the cerebral cortex, in what is known as the mentalizing network, which is important for thinking about others’ thoughts, feelings and intentions, said Darby Saxbe, a professor of psychology at the University of Southern California and author of “Dad Brain: The New Science of Fatherhood and How It Shapes Men’s Lives.”
When Saxbe and her colleagues put 40 first-time fathers in brain scanners before and after their child was born, they found a reduction in gray matter volume in regions of the mentalizing network. These brain areas seem to overlap with where mothers’ brains also shrink, though the volume reduction is less. (Mothers also experience changes in other areas of the brain, including the amygdala, which is important for emotion processing.)
Knowing that our brains are shrinking may add more stress for already stressed-out parents, but these changes point to a form of neuroplasticity that is adaptive and linked to better parenting engagement and experiences.
“Shrinking sounds bad, but it’s not,” Daneshnia said. “It’s usually a requirement for optimization of the brain.”
In a 2024 study, Saxbe and her colleagues found that the reduction in gray matter was correlated to the amount of time dads spent with their infant, as well as their bond with and enjoyment of their infant.
“I like to say it’s not just shrinking, it’s not necessarily loss,” Saxbe said. “It’s more like efficiency and retuning, like upgrading.”
Changes to the brain’s mentalizing network may help fathers and mothers adapt to the challenges of figuring out what that new little human wants and needs (preferably before they have a meltdown).
This shrinking parent brain differs from the atrophy found in neurodegenerative disease or aging because the locations and magnitude are different, experts said.
In mothers, there’s also a rebound in gray matter in the days and weeks following childbirth, though reductions in some brain regions have been detected at six years postpartum.
While there’s not enough data yet, Saxbe suspects it’s a similar pattern in fathers. In a 2023 study, Saxbe and her colleagues found that fathers who had the biggest volume increase in the hippocampus, a brain structure important for memory and navigation, had stronger bonds with their child, more affectionate attachment and lower parenting stress.
Some of the brain changes linked to full participation in parenting may also expose vulnerabilities for paternal postpartum depression and anxiety, Saxbe said. Paternal postpartum depression occurs in roughly 1 in 10 fathers, while maternal postpartum depression occurs in up to 1 in 5 mothers.
Parenthood is “meaningful and blissful, and it is also frustrating and exhausting. All the pros and cons are there for dads as well as for moms,” said Saxbe, who has two teenagers.
But in the long run, parenthood may be neuroprotective for the aging brain, according to a 2025 study that analyzed data from the UK Biobank of more than 19,000 females and 17,000 males. Parents who had more children had increased functional connectivity in brain networks that tend to become sparse with aging.
It may feel ironic to sleep-deprived parents, but they may end up with “younger-looking” brains.
A brain for rewarding connection
Fatherhood also shapes how different brain areas communicate with one another.
In a longitudinal study published in May, Daneshnia and her colleagues scanned the brains of 25 fathers right after their child was born and up to 24 weeks afterward. They discovered that there was a shift in connectivity toward higher cognitive and emotional processing brain areas involved with empathy and reward, Daneshnia said.
Importantly, there is evidence that fatherhood changes brain function, especially in circuits involved in parental motivation, said James Rilling, a professor of psychology at Emory University and author of “Father Nature: The Science of Paternal Potential.”
In a recent study, Rilling and his colleagues had 51 expectant fathers look at photos of infants while getting their brains scanned. First-time dads looking at pictures of infants had larger increased activation of brain areas involved in empathy as well as in the dopamine reward system compared with non-dads.
Interestingly, the stronger brain responses correlated with the dad’s involvement level in hands-on caregiving, such as bathing and changing diapers. Other research Rilling conducted found that fathers had stronger responses in the ventral tegmentum area, a key reward region in the brain, when looking at photos of their own toddler compared with ones of an unknown infant or adults.
Gay fathers also had similar activation in emotional processing centers of the brain as mothers who were primary caregivers, another study has found.
These dad brain changes are not universal, reflecting the wide range of fathering behavior. Some men never meet their child, while others become the primary parent, and the extent of brain changes seems to reflect the level of involvement, Saxbe said.
Mothers, on the other hand, are more “obligate,” and their brain changes are generally larger, she said. While cultures have differing expectations of fathers, “there are no cultures where mothers are fully hands-off.”
(Indeed, while biomedical research has largely focused on males with only recent pushes to include more women, one of the few exceptions is in the study of parenting and child-rearing.)
“Men’s neurobiology is dynamic, but it fluctuates depending on Dad’s level of engagement,” Saxbe said.
The hormonal shifts of parenthood
The brain remodeling that fathers experience may be in part driven by changes in their hormones, Saxbe said.
While fatherhood may be considered traditionally masculine, perhaps surprisingly it is associated with lower male sex hormones. Many studies show that fathers have lower testosterone levels than non-fathers of similar age and background.
While men with higher testosterone were more likely to become partnered fathers, they experienced larger declines in testosterone than single non-fathers, one study found. Indeed, fathers who spent a significant amount of time on child care had lower testosterone levels than those who were not involved.
Even from the earliest point in the parenthood journey, when the first child was mid-gestation, the soon-to-be fathers already had lower testosterone, Rilling and his colleagues found in a 2025 study.
This was a surprise because Rilling thought these biological shifts would be the result of interactions with the infant. But it could be that “when these men recognize, ‘I’m gonna be a father,’” Rilling said, “there’s some kind of psychological and hormonal shift that occurs.”
The fathers also had lower levels of vasopressin, another hormone important for social behavior and bonding.
Like the brain changes, these hormonal shifts predicted how involved dads were: Lower testosterone levels predicted more time spent with their partner (and, presumably, their newborn) while lower vasopressin was linked to more engagement with the infant.
A father’s levels of prolactin, a hormone primarily known for milk production, during his partner’s pregnancy also predicted the dad’s more positive attitude toward parenthood, less parenting stress and more enjoyment of the infant, Saxbe found in another study.
There is mixed evidence about how oxytocin, a key hormone for social behavior and bonding, changes in fatherhood. For mothers, oxytocin increases dramatically during pregnancy. Fathers with higher levels of oxytocin physically interact with their infants more and exhibit more social engagement and emotional synchrony.
In one double-blind study, researchers infused oxytocin directly up 35 fathers’ noses, which caused the dads to physically and socially engage more with their 5-month-old infants compared with a placebo infusion. At the same time, the infants’ oxytocin also increased. They played more and looked at their dads more.
“Oxytocin kind of stimulates this positive feedback cycle that leads to father-infant bonding,” said Rilling, who has two kids.
Taken together, the science of dad brain is really a look at how we adapt to one of the biggest changes in life.
“I think it’s apt to call it a parental brain,” Saxbe said. “Some of these are universal adaptations of parenthood.”
These neural adaptations are a whole family affair.
After all, the child’s brain is changing alongside their mother’s and father’s, as we emerge into a new world, trying to figure it – and each other – out together.