ONE WILD WORLD — NEWSLETTER

Issue #027   ·   Useless But Fascinating   ·   June 2026

The “mommy brain” cliché has been doing the rounds for decades — the forgetfulness, the scattered thinking, the sense that something important drained out of your head along with everything else. Neuroscience has now spent twenty years building the evidence to respond to it. The response is: yes, parenthood changes your brain — permanently, measurably, and in ways that can be detected from a brain scan years after the birth. But the change is not what the clichié describes. It looks considerably more like what happens during adolescence than like anything resembling decay. And it does not just happen to mothers.

BY THE NUMBERS

4.9%

Maximum reduction in cortical gray matter volume during a first pregnancy — measured across 179 women in a 2025 study published in Nature Communications. Changes tracked from before conception through the postpartum period.

94%

Share of the brain's total gray matter regions that show measurable change during pregnancy. In a 2024 study in Nature Neuroscience, one researcher scanned her own brain throughout her pregnancy and found that "few regions were untouched by the transition to motherhood."

6 years

How long after birth the pregnancy-related brain changes remain detectable. A 2021 follow-up study could identify whether a woman had ever been pregnant — from a brain scan alone — with 91.67% accuracy, six years after delivery.

1%

Average gray matter reduction in first-time fathers. Same type of change as in mothers, less pronounced, concentrated in the cerebral cortex. No pregnancy required.

~40

Expectant fathers scanned in Darby Saxbe's 2023–2024 study. Finding: the more engaged a father was with caregiving, the greater his gray matter loss. The brain was tracking commitment.

For most of the twentieth century, the “mommy brain” phenomenon was treated as a straightforward loss. Pregnant women reported forgetfulness. Surveys confirmed it. The explanation was hormonal disruption, sleep deprivation, the general chaos of new parenthood. Nobody looked at the brain itself.

That changed in 2017. A team of researchers in the Netherlands, led by neuroscientist Elsje Hoekzema, published a study in Nature Neuroscience that did something no one had done before: they scanned first-time mothers before pregnancy, shortly after birth, and then two years later. They found that gray matter had reduced in specific, targeted regions — not randomly, not diffusely, but concentrated in areas linked to social cognition and the capacity to read another person's mental state.

Two details from that study are worth sitting with. First, the changes persisted for the full two-year follow-up period. Second, the regions where gray matter reduced most strongly were exactly the regions that activated most powerfully when mothers looked at photographs of their own infants. The brain had not decayed. It had been remodelled. The areas most changed were the areas doing the most work.

Gray matter was lost in precisely the regions that lit up most when mothers looked at their own children.

"Your brain shrank" sounds alarming. It is worth being precise about what that actually means, because the popular interpretation — cognitive decline, degraded function, thinking slower — is not what the research shows.

Gray matter is not brain tissue you simply want more of in all circumstances. It is made up of cell bodies and synapses, the connections between neurons. The brain perpetually adds and prunes these connections based on what it is doing and learning. Adolescents experience a well-documented, dramatic loss of gray matter volume across their teenage years — and far from representing decline, this process is understood as the brain becoming more efficient: trimming redundant connections, streamlining circuits, consolidating what it actually needs.

The hypothesis for pregnancy-related gray matter reduction is the same. The brain is pruning. The regions most involved in social cognition, empathy, and reading other people's intentions — the regions that are about to become more important than they have ever been — are being streamlined. In Hoekzema's 2017 study, mothers who showed the most gray matter reduction also scored highest on mother-infant bonding measures and showed the strongest neural response to their infants. More loss, more connection.

A 2024 study in Nature Neuroscience made the case more vividly than any before it. The lead researcher, Elizabeth Chrastil of UC Irvine, used her own pregnancy as the subject — undergoing MRI scans every few weeks for years, from before conception through two years after birth. The data were dense, longitudinal, and unambiguous. Widespread, lasting decreases in gray matter volume, across nearly the whole brain. And no corresponding evidence of cognitive decline.

Here is the part of this story that has gone almost completely unreported, which is curious, because it may be the most surprising finding of all.

Fathers' brains change too.

No pregnancy. No hormonal flood of gestation. No direct biological experience of the process. And yet: brain imaging studies on expectant and new fathers show the same type of structural changes seen in mothers — gray matter reductions concentrated in the cerebral cortex, the region responsible for executive function, reasoning, and social processing. Less pronounced than in mothers. But measurably, structurally, really there.

The most detailed evidence comes from Darby Saxbe, a psychology professor at the University of Southern California, and her colleagues in Spain. In a study published in Cerebral Cortex in 2023, they scanned 40 expectant fathers before and after the birth of their first child. They found gray matter loss — an average of about 1% of volume in the cerebral cortex. In a follow-up in 2024 looking at 38 first-time fathers, they added a critical variable: the fathers who reported stronger bonding with their baby before and after birth, who planned more time off work, who spent more time with their infants, who felt lower parenting stress — all of them showed greater gray matter reduction than less-engaged fathers.

The brain was tracking commitment. More involvement, more change.

The fathers who lost the most brain volume were the ones bonding most closely. The brain was recording the relationship.

There is a hormonal dimension to this as well. Multiple studies find that testosterone drops in new fathers — and that the drop is proportional to time spent in caregiving. This runs counter to the instinctive association of testosterone with male competence and capacity. What the research suggests is almost the reverse: the hormonal shift appears to reduce certain socially competitive drives and, according to researchers who study it, enhance neural plasticity and sharpen sensitivity to infant signals. Lower testosterone, better ears for a baby's cry. The body preparing a father for what is about to be asked of it.

Developmental neuroscientist Helena Rutherford of Yale put it plainly: "We've acted as though once the baby arrives, men simply become fathers. But actually, the psychological, neurological, and hormonal changes that start to unfold in them during pregnancy are on a parallel path with the mothers."

Hoekzema's 2017 study followed mothers for two years after birth. The gray matter reductions showed partial recovery — the brain did not stay at its pregnancy-low — but the changes were still detectable at the two-year mark. That left an obvious question: does the brain eventually return to baseline?

A 2021 follow-up answered this, at least provisionally. Researchers examined the brains of women six years after delivery. The changes were still measurable. A classifier trained on the brain scans could determine whether a woman had ever been pregnant — from a single scan taken six years after giving birth — with 91.67% accuracy. Six years on, the brain retained a detectable record of parenthood. The paper's authors described the changes as likely permanent and argued that pregnancy history should be routinely collected as a standard variable in all neuroimaging research going forward.

A 2024 study published in Scientific Reports pushed the picture further. When researchers looked at the brains of older mothers — women well past their childbearing years — they found that mothers tended to have higher gray matter density across wide regions of the brain compared to women who had never given birth. The overall picture this suggests is a U-shaped trajectory: volume reduces during and after pregnancy, partially recovers, and in the longer term appears to end up above baseline. The brain gives something up, then builds back with interest.

The most recent finding in this field was published in PNAS in early 2025, and it would have been difficult to predict from first principles.

Researchers analysed the largest population-based neuroimaging dataset available — tens of thousands of participants — and examined how the number of children a person had correlated with brain-wide functional connectivity in middle and later life. The finding: parents of more children showed higher brain connectivity, particularly in networks linked to movement and sensation. And — this is the striking part — the brain regions where parental connectivity was highest were precisely the regions where age-related decline is typically strongest. The changes associated with having more children appeared to counteract the changes associated with ageing.

This is a correlational study, and it carries the usual caveats. People who have more children differ from people who have fewer in dozens of ways that are hard to fully separate. But the finding is consistent with the broader pattern emerging from parental neuroscience over the past decade: the structural changes that come with parenthood do not look like a cost. They look like an investment.

The “mommy brain” framing is not entirely wrong. The brain does change when you have a child. It changes structurally, measurably, and in ways that persist for years — possibly permanently. The sleep deprivation and cognitive load of early parenthood are real, and they do affect working memory and attention in the short term.

What the framing gets wrong is the interpretation. The structural changes are not random damage. They target specific regions — the ones most needed for reading another person's mind, for bonding, for social attention. They occur in fathers who engage as well as in mothers who give birth. The more a parent shows up for caregiving, the more the brain changes to support it. And the long-term trajectory, from the evidence now available, appears to be net positive: a brain that is more functionally connected, more attuned, and possibly more resilient against the cognitive effects of ageing.

Parenthood rewires the brain. The research says it does so not as a side effect or a degradation, but as a targeted adaptation to the most cognitively and socially demanding role most humans will ever take on.

Gray matter reduced in exactly the regions that light up when a parent looks at their child. A brain scan six years later still records the experience. The more a father engages, the more his brain changes. Nobody is declining. Everyone is adapting.

The folk wisdom had the mechanism right and the meaning exactly backwards.

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SOURCES

Hoekzema, E. et al. — "Pregnancy leads to long-lasting changes in human brain structure", Nature Neuroscience (2017)

Hoekzema, E. et al. — "Do pregnancy-induced brain changes reverse? The brain of a mother six years after parturition", Cerebral Cortex (2021)

Pritschet, L., Taylor, C.M. et al. — "Neuroanatomical changes observed over the course of a human pregnancy", Nature Neuroscience (2024)

Servin-Barthet, C., Martínez-García, M. et al. — "Pregnancy entails a U-shaped trajectory in human brain structure linked to hormones and maternal attachment", Nature Communications, 16:730 (2025)

Martínez-García, M. et al. — "First-time fathers show longitudinal gray matter cortical volume reductions: Evidence from two international samples", Cerebral Cortex (2023)

Saxbe, D. et al. — "Cortical volume reductions in men transitioning to first-time fatherhood reflect both parenting engagement and mental health risk", Cerebral Cortex (2024)

Rotondi, V. et al. — "Long-term effects of motherhood on brain structure", Scientific Reports (2024)

Ward, P.G.D. et al. — "Protective role of parenthood on age-related brain function in mid- to late-life", PNAS, 122(8) (2025)

Kim, P. et al. — "Neural plasticity in fathers of human infants", Social Neuroscience (2014)

Feldman, R. — "The neurobiology of human attachments", Trends in Cognitive Sciences (2017)

Saxbe, D. — "Dad brain is real — and it's a good thing", New York Times (June 2024)

Rutherford, H.J.V. — quote sourced via Harry & David / The Table feature on paternal brain research (2024)

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