What really happens to a mother's brain

The latest studies point to both change and recovery in new moms

Happy Mother’s Day! At exactly this time last year, I was in Spain, at a cafe on the sand of the Iberian Sea, eating grilled shrimp and pan con tomate, about to order an Aperol Spritz. This year, I’m in bed in my sweatpants, having just eaten a fried egg sandwich cooked by my 14-year old. Both meals were great! I’m hoping my son cleaned the kitchen after making the sandwich, but definitely don’t want to get out of bed to find out.¹

The reason I was in Spain last year is that I was at the Parental Brain conference, the 8th ever meeting of the world’s only conference devoted solely to the neuroscience of parenting. This also gave my husband and I a great excuse to go back to the neighborhood where we spent fall semester 2019 on a Fulbright and re-visit our old haunts. Here I am around the corner from our old apartment.

At the conference, I got to join a panel presenting on the paternal brain, and also got to see a keynote talk from Susana Carmona, who has done some of the most important research on the maternal brain. Susana is profiled in my book as a key collaborator and one of the inspirations for my research, and she also has her own book coming out in English this fall (the original Spanish version, Neuromaternal, has been out for a while). She and her collaborator Elseline Hoekzema published a landmark 2017 paper that stunned the neuroscience community. Their big finding: Women lose brain volume across the transition to motherhood, in ways that are so striking that a machine learning algorithm can tell non-mothers apart from mothers. Although a smaller brain sounds bad, Carmona and her collaborators have linked this brain volume reduction to better mother-child bonding, suggesting that a shrunken brain may work more efficiently to process social information from the infant. Moreover, brain volume loss did not impair cognitive performance in their sample of women. Indeed, the areas that lost the most volume are in regions implicated in social cognition and empathy, which are important in infant care. This helps support the “adaptation vs deficit” interpretation of their findings.

Post-conference dinner. Yellow arrows pointing to me & Susana

I actually live-blogged three sets of conference talks from Spain last year, including my panel, a talk on animal fathers, and Susana’s keynote, but I had about 200 subscribers at the time, so I’m going to tell you about Susana’s talk again, because I think this is such cool work that any mom with a brain should know about.

Carmona’s body of work is a master class in how to develop a program of research. After her initial study finding that the human brain changes over the transition to motherhood, she conducted a series of studies that branch out from this discovery, interrogating questions that deepen our understanding of the maternal brain. These include:

Are the brain changes similar to those taking place during adolescence?

Yes! Carmona and her team pursued this work because early media coverage of her maternal brain findings used an implicit deficit model, referring to brain “atrophy.” She wanted a more developmental frame instead, one that might reflect normative adaptation to a life stage. She contrasted her sample of mothers with a sample of adolescents followed across puberty, finding very similar magnitudes of brain volume change. In other words, the transition to motherhood is a window of plasticity and restructuring that resembles the transition to adolescence.

Do these brain changes reverse?

It seems like they persist instead (but read on for more about their time course). There is evidence that smaller brain volume persists in mothers followed two years after birth, compared to a comparison sample of non-mothers. Carmona’s team has even found smaller brain volumes in mothers six years after birth, although the latter study should be taken with a grain of salt; it had a very small sample given that many moms in her sample had more than one child and many of the non-mothers had become mothers by the six-year follow-up.

Do fathers undergo similar brain changes?

Yes- similar, but not exactly the same. In our first pass at this research, we combined data from Spanish dads drawn from Susana’s study (the partners of mothers in her sample) and the dads we scanned at my lab. Both samples were comprised of first-time fathers followed from before to after birth. We found similar brain changes as the mothers, but they were less striking and significant overall.

What is the temporal course of the brain changes?

This gets really interesting. Susana’s group has published some elegant recent work suggesting that the trajectory of brain change across the transition to first-time motherhood is not linear, but rather U-shaped. Take a look at the graph above, and you’ll see that brain volume dips right before birth in mothers (the orange line) but not in non-mothers (green line) or the female partners of the gestational mothers (“non-gestational mothers”; blue line). The structures then recover in size in the first six months after birth, such that the mothers regain some brain volume but still have slightly smaller brains at postpartum than before pregnancy.

The U-shaped pattern that Carmona’s group uncovered is uncannily similar to the results of an intensive longitudinal neuroimaging study in which a single, heroic mother underwent 26 MRI scans, starting three weeks before pregnancy and finishing two years after birth. As you can see from the figure below, her grey matter volume, cortical thickness, and overall brain volume all dipped around birth and then slowly rebounded. In other words, the story of the maternal brain is not one of overall volume loss, but rather of shrinkage followed by a bounce-back.

Are these changes mediated by gestational hormones?

Yes! In the same paper that reported on the U-shaped trajectory of maternal brain volume, the authors also linked that trajectory to changes in estrogen across pregnancy, with estrogen rising as brain volume decreases in a mirror image. The figure below shows decreasing brain volume (orange line) and increases in two sulfated estrogens. In other words, the brain gets smaller as these estrogens increase, and then rebounds when estrogen drops. (They also tested some other androgen and estrogen hormones that did not track with brain change).

Do brain changes relate to postpartum depressive symptoms?

Yes! One study found that when the amygdala increased in volume from prenatal to postpartum, women reported more postpartum depression. There’s a lot more to say about perinatal depression and the brain, and about how the parental brain looks in old age (spoiler: parenthood may be neuroprotective), so I’ll save those topics for future posts. I’m also working on writing up some new work from Elseline Hoekzema’s lab on what happens to the brain of second-time moms, so stay tuned!

Whether you’re drinking cocktails by the beach or hiding in bed this Mother’s Day, I hope that you are having your best possible day and getting as much appreciation as you deserve.

1. Update! He did!!! Best Mother’s Day ever.