“Dad brain”: How becoming a parent changes the brain, with Darby Saxbe, PhD

Before we get started today, I'd like to take a moment to ask you to fill out our listener survey. We'd like to learn more about you and what you think of speaking of psychology. So if you would, please go to at.apa.org slash SOPSurvey. That's at.apa.org slash SOPSurvey.

Thank you. We really appreciate it. Now on to the episode. For many new parents, the first weeks and months after their baby is born are a time of deep bonding and bewildering changes. Between sleepless nights, scrambled schedules, and learning to meet the needs of a tiny infant, many new fathers and mothers feel like their world has been turned upside down overnight.

Now it turns out those changes may go even deeper than parents realize. In recent years, scientists have found evidence that becoming a parent can change the structure and function of a person's brain. And crucially, these changes happen to fathers as well as to mothers. So how does parenthood change us? What brain hormonal and other shifts occur in new moms and dads?

Do these changes look different in men than in women? Or does becoming a father or a mother change the brain in the same way? What advantages and risks might these changes confer? And what does this research suggest about the best ways to support people through the transition to parenthood to benefit both parents and children? Welcome to Speaking of Psychology.

the flagship podcast of the American Psychological Association that examines the links between psychological science and everyday life. I'm Kim Mills. My guest today is Dr. Darby Saxby.

Dr. Saxby is an associate professor of psychology at the University of Southern California, where she leads the neuroendocrinology of social ties or NEST lab. She's interested in how close relationships affect health. particularly during major life changes such as the transition to parenthood. She has studied brain changes in both fathers and mothers and how those changes are correlated with hormones and behavior.

Her research has been featured in media, including the New York Times, the Washington Post and NPR. And she's working on a book called Dad Brain, slated for a release next year. Dr. Saxby, thank you for joining me. I'm very happy to be here. Thank you for having me.

I mentioned that you're working on this book, Dad Brain, and people might have heard the term mom brain or mommy brain before, maybe used in a pejorative way. But what do you mean when you talk about dad brain or mom brain? Right. So what we're starting to discover, and there's this small but emerging neuroscience literature in humans, is that the brain is remodeled by parenthood.

And we've known this for a while. If you look at rodents, if you look at primates, that you see changes that are linked with adaptations that support nurturing a new infant. And it was really in 2016, there was a group in Spain that first looked longitudinally at moms who were recruited before becoming pregnant. And then...

scanned for a second time a few months after the birth of an infant. What they found is going to sound like a bad joke, but it's actually, we think, a good thing, which is the brain got smaller. So it lost some gray matter volume between that first preconception time point and the postpartum scan. And we think that might be a process of streamlining and helping the brain work more efficiently when it comes to all the processing of social information that new parents have to do.

So, in much the same way that the brain actually loses volume in early childhood, as connections are formed and pruning occurs. So areas in which the moms lost brain volume were those linked with mentalizing and social cognition. And moms who lost more volume subsequently reported stronger bonds with their infants. So I, at the same time that this study was coming out, was collecting data from dads who were transitioning to parenthood. So in our lab in California...

We recruited couples who were expecting their first child. We scanned the men in mid-pregnancy and then again about six months postpartum. So our time frame was a little bit different from the group in Spain. But when I saw that the Spanish group had a sample of male partners of the women that they had followed, I immediately, well, not immediately, it took a few months, I got a Fulbright, I hopped on a plane, I went to Spain.

And I tried to convince them to collaborate with me. And eventually, we were able to pool our samples. So we took the first 20 deaths from my sample, the 20 deaths that they had scanned. and found that across these two samples, we saw changes in the men that were actually really similar to the changes that they had already observed in the moms.

And there were a few differences. One was that the changes were more subtle. They were less striking. They were less significant. So with the moms, you can use a machine learning algorithm. that will basically tell you whether a mom is pre- or postpartum just based on the brain structure. With the dads, we didn't see effects that were that striking. And the other difference was that in the moms, you saw changes to...

The cortex, which is sort of the top layer of brain tissue that does a lot of our higher order thinking, and the subcortex, which is more kind of our lizard brain that includes the amygdala and some of our more sort of emotion processing regions. In the dads, we only saw changes to the cortex. So that was our big finding. And then I've subsequently replicated that in my lab with a bigger sample of the dads that I've scanned and connected that with some.

parenting measures and other measures that we've collected in our dads. Does that brain volume come back or is this permanent? That is an excellent question that we don't really know the answer to. So the Spanish group actually did scan some of the moms seven years after the birth of their child.

And they found that there was some retention of the brain volume losses. There was rebound in areas like the hippocampus, but the brain overall was still a little bit smaller, or I like to say like leaner and meaner, than it was before pregnancy. So I should say, though, that because it's hard to track people down after seven years, they had a really small sample. I want to say it was like maybe a dozen moms that they were able to scan again.

So we're now actually scanning the fathers in our sample. We're doing a seven-year follow-up. And hopefully when we finish acquiring that data, we'll be able to answer some questions about that in men.

Now, this is after the birth of the first child in a household. Do we know what happens with subsequent births if there are more kids? Yeah, also a great question that we don't have the answer to. So I should emphasize this literature is really small. It's really emerging. So we will be looking at that with our seven-year follow-up because some of our kids do have siblings. I would say a little over half now have a sibling or two.

There was one study done by Pil Young Kim at the University of Denver that looked at fathers who were followed from one to four months postpartum. So all the dads were scanned after birth, but she scanned. twice in that early postpartum period. And she had a mix of first and second time dads, but the sample was too small to really look at group differences.

One of the questions that I would be really curious about is, did dads lose more and more volume? Does the brain get more and more streamlined? Or at a certain point, is there more rebound once you have more kids?

You've also looked at hormonal changes that can occur in men when they become fathers. Can you tell us more about that research? What are some of the changes that you found and what are the everyday impacts? Yeah, so often when we think about hormones and parenthood, we think about pregnancy and birth, right, which we know are really hormonally.

rich events, but there's plenty of evidence that we see hormone changes in men as well. One of the biggest hormones that has been studied is testosterone, which we know of as a hormone that's linked with power, status, dominance, male secondary sex characteristics. It's very much associated with men, even though women also have detectable testosterone levels, but men's levels are many times higher.

And we know from looking at bi-parental animals like rodents and primates that there are testosterone drops around the birth of offspring. And we actually see the same thing in humans. And so one of the most kind of impressive studies to look at this was done by Lee Gettler, who's at University of Notre Dame. This was a really big study from the Philippines.

And they followed men over time. They had testosterone measures from when the men were in their 20s. And then they looked again years later. And they found that men who were residing with children, especially men who were spending more time caring for children, had lower testosterone. And that study helped answer the chicken-egg question of, you know, is it that lower testosterone men are selected into parenthood so they started lower and they stay lower?

Or is there something that's changing? Because they had this longitudinal data, they were able to say, actually, the men who became fathers had higher testosterone before they became dads. And then they showed more of a decline. So it really seems like there's a change over time that is linked with becoming a father. And I've replicated that result in my lab. We've measured testosterone in our dads.

And we found that lower testosterone and a drop in testosterone are linked with more motivation to participate in baby care and better relationship quality across the transition to parenthood.

So there are some benefits then to the changes in the hormones. For men, I'm hearing what they are. What about for women? How do their hormones change? Yeah. So actually, we found that... not only do women's hormones change, but they're also responsive to the changes in their partners. So we did a study where we looked at postpartum depression in both the mothers and the fathers.

We found that when dads had lower testosterone about nine months after the birth of a child, they reported more depression, but their partners actually reported less depression when they were with lower testosterone men. So there's a bit of a like good for the goose, not good for the gander kind of situation happening. And that effect for moms was totally mediated by relationship satisfaction. So if you're a new mom.

you have a partner whose testosterone is maybe dropping in an adaptive way around the birth of a child, that might set you up to have sort of better co-parenting relationship and be buffered against depression. But there might be some mental health risks for men. that, you know, I think we need to understand more. The kind of takeaway from that paper, though, was that there is a happy medium. Like, men were doing worse at...

both very high and very low levels of testosterone, but there are a lot of men in the middle that seem to be a low risk for depression. So I wouldn't want men to listen to this and think, you know, like... I'm going to have terrible mental health because of testosterone drops around the birth of the baby. For the most part, it seems like these hormonal changes are really adaptive.

And I'm thinking also there are some men who may hear something like this and say, yeah, but what happens to my sex drive, right? Yeah, well, and we know that the transition to parenthood is a big kind of reorganization of the couple's sexual activity, right? Because often there's prohibition against having sex in the first few months after birth.

And, you know, there's change in desire. If the mom's breastfeeding, she may not want to be touched, right? Like there's a lot that's going on kind of in terms of the couple relationship. So, you know, a temporary drop in sex drive might not be the worst thing in the world. And when we're thinking about evolutionary theory, we think about what is the trade-off between mating and parenting.

So if we're sort of in a mating place, we want to have as many babies as we possibly can. We want to maximize our opportunities to reproduce. Whereas if we're more in a nurturing mindset, we want to take care of the... babies that we do have and ensure that they live to adulthood. And as societies get richer and more stable, it's actually more adaptive to...

use that sort of more nurturing repertoire. You don't need to have a dozen kids in hopes that a couple of them will survive. You actually tend to put a lot of investment into just a couple of kids. And we see that in industrialized societies that family sizes get smaller. And that's kind of accompanied with a shift in how people enact their reproductive strategies.

Let's talk for a minute about sleep as a factor in some of these changes. I mean, the first few months of parenthood generally involve a lot of sleep deprivation. Could that be another factor in these brain changes? Absolutely. And I think that's kind of the, anytime I tell anybody about any of this work with brain hormones or mental health, they always say, well, right, it's probably because of sleep deprivation.

And so we've measured sleep in our lab. We found that when dads have more brain gray matter volume reduction, they also report worse sleep. But it seems like the sleep is actually not the cause, but the consequence of brain change. So we find that men who lose more gray matter volume across the transition to parenthood actually don't have worse sleep before birth.

but they have sort of increasingly worse sleep after birth. So when you're sort of teasing out that direction of causality, it's a little bit hard to know what happens first, brain reorganization or sleep changes. Because when we're more motivated and engaged in parenting, we have worse sleep, right? Because we're getting up more often with the baby. And therefore, our sleep is more disturbed.

My understanding of the term mommy brain also refers to the fact that some women after giving birth start to feel like, I can't remember anything. I don't know where I put my keys. What am I doing today? It's the same thing happening to men under these circumstances.

Yeah, so there's actually this growing literature looking at cognitive changes with motherhood. And, you know, like you said, like mommy brain is often kind of disparaged as like this thing that makes you less smart. There's actually a lot of evidence that you sharpen your cognitive. functioning after motherhood in the sense that you have more ability to remember and retrieve things that are specific to your infant, right? So like if you think about a rodent...

who has a whole bunch of babies running around, you can kind of forget where you put them. And so like, there's a lot of stuff with like smell and the hippocampus that's linked with pup retrieval, like being able to find your pup, smell them and bring them back. And in humans, obviously we're not smelling our babies who have left the premises. We do need to remember a lot of different things when we're parenting in the early days and to be responsive to the specific stimulus of the baby.

It may be the case not that we're becoming more forgetful, but actually just that we have more things to monitor. And so there's a paper Jodi Poluski, who's at the University of Rennes in France, wrote that it says it's time to rebrand Mommy Brain. We should actually think of it in a lot of ways as becoming more sharp and specific when it comes to certain things. You might have better retrieval of baby-specific cues, but worse retrieval of other things that aren't as important.

And my hunch is no one has really studied cognitive function in dads, but I think we would probably see something similar to the extent that you're engaging in caregiving. You're tracking a lot of information relevant to your baby. And so you might be losing your handle on some of the other things, some of the other pieces of information that you're trying to keep track of.

And I think the really interesting thing about all of this is that there's this increasing body of evidence that parenthood is neuroprotective in late life. So work from the UK Biobank and other sort of big data sources. are linking number of children with markers of what we consider to be a younger-looking brain. And this is true in both men and in women, which tells us that it isn't just a pregnancy hormone thing, it's like a caregiving experience thing.

that the brain actually, if you use a sort of age-adjusted algorithm to estimate how old the brain looks... it looks relatively younger among people that have had more kids. So whatever's happening to the brain in early parenthood, it's hard to know whether it's good or bad, but it seems like, you know, at the end of the day, you get some benefits.

How did you first become interested in this line of research? I've always been really fascinated with families and parenthood. I think my parents are divorced, so I was always very interested in marriage and how couples.

figure things out because I sort of, you know, like any psychologist, research is me search and you want to understand the things that would fix your own life. And so as a graduate student, I joined this lab at UCLA that was working with the data from the Center for Everyday Life. Lives of Families, which was this big kind of psychology, anthropology, linguistics, archaeology collaboration where we basically went into families' homes for a week.

And we followed them around. We wrote down everything they did. We took their stress hormones. We asked them lots of questions. And it was just this really interesting corpus of data kind of observing family life. And I was very interested in stress and parents and especially parents with kids, how they were managing the household.

I thought, if I'm going to have any hope of trying to make things better, I want to maybe go back to the origin of when the family is first formed to try to understand, are there ways to prevent stress and adversity before they... arise so that got me very specifically interested in transition to parenthood and as kind of a couple's research i was interested in that like how does a dyad become a triad and what does that do to the couple so i'm sort of like a backwards

child development person in the sense that I start with the parents. We think of sort of developmental windows in infancy and early childhood, but I think there are also developmental windows when people become parents. the brain's also changing, hormones are also changing, your social roles are also changing. So I'm actually interested in the adult side of the equation because I think if you don't have...

good healthy parents, you don't have good healthy kids and then it affects the whole society. So I'm kind of going at it from the other side of the equation. How do the brain changes around parenthood compare with brain changes at other stages in life? Does brain structure generally change throughout adulthood or the changes that you see?

with the transition to parenthood very specific and unique? Yeah, so it's hard to have great research designs to measure that because a lot of the studies out there are small and they don't always have control groups. So, you know, if we were to just track...

people in their early 30s for a couple years would we see remodeling similar to what we're picking up on in parents? I don't think so because it seems like we're seeing these consistent changes that aren't necessarily tied to chronological age. But the question of how dynamic is the brain structurally across the lifespan is one that we still need to understand better. I will say like the Spanish group did a study where they compared brain changes in adolescence.

with brain changes across pregnancy and early postpartum, and they found that they were of similar magnitude. So we think of adolescence as this window of neural remodeling. And it seems like the transition to parenthood is sort of a third window. Like if you think of early childhood as your first window, right? Like infancy, the brain is growing and remodeling. Adolescence is your second window.

Transition to parenthood is your third window where there's kind of enhanced neuroplasticity. And that would make evolutionary sense because we have this whole repertoire of behaviors that we need to learn and we need to derive reward from in the same way that in adolescence.

We need to individuate. We need to create peer relationships. There's a lot that we need to be able to do in adolescence that's distinct from what our jobs were in childhood. And I think that's true of the transition to parenthood. And then I think there's another window of remodeling around aging, where you also see a lot of variability. You see some adaptive changes. We're just starting to figure out what is happening with the menopausal brain. Like women have been so understudied.

In our brain research, we don't know enough about brain health in women, but that's another time when you see changes in hormones. And so there's a lot of potential, I think, to better understand these windows of plasticity. We're going to take a short break. When we return, we'll talk about how paternity leave affects stress and mental health for fathers and mothers.

Another area you've looked at is the impact of paternal leave, not just on dads, but on moms as well. What did you find? Let's talk about that. So we were lucky to be in California where we were. collecting our data because not every state has this, but California does have a disability leave option for dads. So about half of the dads in our sample had some kind of access to paid paternity leave.

And when we looked at just a simple kind of group difference between dads who did and didn't have access to paid paternity leave... We looked at prenatal to postpartum stress, mental health, and sleep. We found that dads had some benefit from the access to paid leave, like they had, you know, better trajectories of sleep and stress.

But it was really the moms that had the biggest benefits. So they had better trajectories of depression. They were less likely to develop postpartum depression. They were less stressed and they had better sleep across the transition to parenthood. I think of paternity leave as one of those things that really benefits not just dads, but the whole family. We know that it has benefits for kids. We also know that it has benefits for the partner.

And I think anything as a stress researcher, it's like anything you can do to relieve stress on the family system. So any form of paid leave, whether to mom or to dad, I think can be really beneficial. And you certainly see that. In other countries where there are sort of paternity leave incentives or take up programs that nudge more fathers into taking leave.

It sounds to me like there should be some public policy implications of this research. I mean, how do we go from the bench to reality? How do we apply this and get the changes that would let everybody benefit from what you're learning? This is what I think about all the time, right? So if we think of this as a window of neuroplasticity, how do we reduce stress, which we know is bad for the brain?

how do we allow space and time for healthy change? Because if you think about every window of change is a window of vulnerability, but it's also a window of opportunity. How do you maximize that opportunity? So I think there's an interesting kind of two-generation frameworks within research. So you're looking at child outcomes, but you're also looking at parental.

mental health and parental psychological outcomes. I think you can't really study kids without considering what's happening for parents. There's so much concern now about this epidemic of youth anxiety and depression. But the fact is you look at parents of young people and they are also struggling. And I think, you know, you sort of need to pay attention to the whole family system.

So what's interesting right now is that there's all this kind of pronatalist talk. Like there was a New York Times article out yesterday saying the Trump administration wants to get people to have more babies. But that isn't coupled with the kinds of policies that would motivate healthy baby having, right? Like we're cutting Head Start at the same time. We're, you know, defunding Medicaid, which is where a lot of births happen.

Why don't we have universal paid family leave for new parents? Every other industrialized country has it, even countries that are much wealthier, much less wealthy than us. have managed to figure out how to give generous family leaves. And there's a statistic that in the U.S., about a quarter of moms go back to work within two weeks of birth. which to me is just complete insanity. Like, what are we doing as a country if we can't allow parents the ability to bond with new kids?

And I think it's like we have this very individualistic framework around parenthood. It's a choice. If you decide to have kids, it's your job. to take care of them and i really need think we need to step back and think about like kids are a public good we want healthy babies we want healthy kids because that's our future workforce that's our national security

Those are the people that are going to be taking care of us when we're old. Whether or not we ourselves choose to have kids, we all benefit from having healthy, happy kids who are growing and thriving. And when we start to think of it as a public good, then I think we can unlock a little more political will for the kinds of policies that we know can support families during times of transition.

You were recently quoted in a news article about the importance of including diverse populations in research. Have you looked at how people's experience of early parenthood varies by race, ethnicity, and socioeconomic status? Yeah, so we know there's a lot of variability in outcomes like postpartum depression, stress in early parenthood that are linked with things like socioeconomic status. We know that...

Poverty is really detrimental, in part because of the family leave piece that we were talking about. And in my studies, because we have pretty small samples, we haven't been able to dig too much into group differences. try to recruit the most diverse and representative sample that we can. But in addition to sort of sociodemographic differences, it's also really important to consider culture.

Because so much of how we parent and how we approach parenting is linked to how we ourselves were raised. And is it normative to have intergenerational households? Is it normative to... parent in a different way. I mean, I sort of think that all of us were designed to raise kids in community and our very isolated model of parenthood is setting us all up to be. unhappy, but you can see a lot of variability across cultures and how people approach that.

Now, we're mostly talking about new parenthood today, but I also want to ask you about an op-ed that you wrote recently. It was published in the New York Times about under-parenting. The idea that giving kids more space to be bored is good. for both kids and parents. What prompted you to write that op-ed and how does it tie in with your research on parenting? Yeah, so I'm a clinical psychologist, but I'm also an extremely lazy mom. And so...

You know, I wanted to write about this idea of giving kids downtime, giving them space to be bored, not letting them get over occupied, because I think one of the things that is causing stress for parents and is actually dampening the birth rate. is this sort of intensive style of parenthood that has really just become prevalent in the last few decades.

Alison Gopnik has written about this. The use of parenting as a verb is actually relatively recent. It's from the 1970s that we thought of parenting as an activity that you do as opposed to just something that you are. So, you know, we have this style that's very effortful. It's always on. It's very child-centered. We take kids to lots of activities. We spend a lot of time shuttling them around. And it's very unusual, kind of historically, if you think about the fact that in lots of cultures

kids aren't necessarily given lots of special activities to, you know, be escorted to. It's more like they're following adults around, they're modeling, they're learning from what adults in the community do. And they're contributing oftentimes very useful labor to the communities. So we sort of have it backwards where I think we're...

rushing around trying to please our kids as opposed to our kids actually learning from us doing the things that we need to do as adults. And my interest in this, like I said, I'm a very lazy mom, but it also just comes from studying parents. and studying stress in parents and thinking about how is it we've crafted this style of parenting and these expectations around parenting that feel pretty unsustainable, I think, for a lot of people.

And what's interesting is if you look at the time diary trends from the 50s to today, we think of the 50s as like this golden age of kind of like June Cleaver, like doting motherhood, wearing an apron, you're always home.

Moms in the 50s actually spent less time per day than moms do now. And what's interesting too is dads are also spending more time than they did in the 50s. So it's like... the kid is just getting a lot more time with parents like we've just you know our model of parenthood is much more time intensive than it was a couple generations ago

You know, and I'm not even that old, but, you know, when I was a kid in the 80s, I would just sort of like roam around my neighborhood and look for a neighbor to play with. And now, you know, the sort of modern style of parenthood is you organize a play date, you set out snacks. You've got crafts ready to go. It's all very curated, but it's not in the service of kids' ability to get unstructured play, which I would argue is kind of the central way that kids learn in childhood.

I'm with you. I'm a boomer. And my mother would say, just get out of the house. I don't care. Just don't hurt yourself. Goodbye. Yeah. Yeah. I mean, it was like if I was home for dinner. Great. Nobody worried. You know, I'm sure my parents had no idea where I was between the hours of 3 and 6 p.m. every afternoon after school.

So what are you working on now? It sounds like there's still a lot of questions regarding dad brains. Do you have more research underway at the moment? Yes. So I mentioned we're doing our seven-year follow-up. So we're bringing the families that we originally recruited in pregnancy.

back to the lab. So the kids are six and seven years old now. The goal is to look at how prenatal stress and adaptation around the transition to parenthood affects child outcomes in middle childhood. And we're having the families do some... interactive activities. They're building a tower with blocks. They're doing an etch-a-sketch. We're looking at sort of joint play and attention. And we're having the families engage in some discussions, too, about how the kid is faring.

how the division of labor is going for the parents. So some of the same constructs that we were looking at in the first wave of the study. So we're about two thirds of the way through collecting that data. Hopefully we'll be able to analyze it and have some results in the next five years or so.

And then my other big thing is writing books. So I wrote the, I mean, it's not out yet. It'll be out next spring, spring 2026, the dad brain book, but I just turned in the manuscript a couple months ago and I'll be working on that with my editor. And I was so fun to write and I just loved it. It was such a delight to not have to write statistics and research articles. Like I love writing research papers, but it was so fun to just get to tell stories and not.

have to worry so much about, you know, going through the peer review gauntlet. And now I'm... writing my second book and it's going to be about this under parenting concept and sort of how not to be a helicopter parent, how parents can relax and enjoy their kids more. So I'm hoping to dive into that soon too.

Well, Dr. Saxby, I want to thank you for joining me today. It's been a lot of fun talking to you. It's been a pleasure. Thank you so much for having me. You can find previous episodes of Speaking of Psychology on our website at speakingofpsychology.org. or on Apple, Spotify, YouTube or wherever you get your podcasts. And if you like what you've heard, please follow us and leave us a review. If you have comments or ideas for future podcasts, you can email us at

speakingofpsychology at apa.org. Speaking of Psychology is produced by Lee Weinerman. Thank you for listening. For the American Psychological Association, I'm Kim Mills.