This Is Your Brain on Motherhood

https://www.nytimes.com/2020/05/05/parenting/mommy-brain-science.html

Version 0 of 1.

When a woman gets pregnant, she can expect a bevy of physical changes to sweep through her body: morning sickness, exhaustion, quickly growing breasts, loosening joints, swelling hands and feet, hair and skin changes, dry eyes and more.

But what happens to her brain? Nobody really knows.

Researchers across the world have begun to chip away at this perennial question, and the results they’ve gathered so far are startling: A woman’s brain, it seems, may change more quickly and more drastically during pregnancy and the postpartum period than at any other point in her life — including puberty. And those brain changes might herald some of the most stereotypically frustrating side effects of giving birth, like that period of forgetfulness during new motherhood, otherwise known as “mommy brain,” and the major mood changes that accompany pregnancy.

In 2002, researchers at the Imperial College of London published a study that involved collecting images of 14 pregnant womens’ brains before and during pregnancy, and a year after they gave birth. They found that certain areas of women’s brains shrunk during pregnancy and others expanded again after delivery. But it was unclear how those changes affected behavior.

In 2016, Elseline Hoekzema, Ph.D., a senior neuroscientist at Leiden University in the Netherlands, published a study in Nature Neuroscience that built on the 2002 study. Dr. Hoekzema and her coauthors conducted M.R.I. scans on the brains of 25 first-time mothers before they got pregnant, and then again in the first few weeks after they gave birth. They compared these scans to brain imaging from 20 women who had not given birth, and found they were starkly different from one another.

The women who had recently given birth had such pronounced biological changes in their brains that a computer algorithm could separate the new mothers from those who had never given birth. In particular, the gray matter in the brains of women who’d recently given birth seemed to be reduced in certain areas, and those changes stuck around for up to two years after birth.

The brain’s gray matter, located mostly in the outer layers, plays a large role in muscle control and in the execution of high-level tasks like seeing, hearing, processing memories and emotions and decision making. The brain also contains white matter, which insulates the axons, helping brain signals travel further, faster and encouraging motor and sensory function. In Dr. Hoekzema’s study, the white matter of pregnant women’s brains did not appear to be changed at all by pregnancy and new motherhood, while gray matter volume was reduced.

Dr. Hoekzema said that these changes might partially occur because of a process known as “synaptic pruning,” a brain phenomenon that eliminates certain connections between brain cells to encourage the facilitation of new connections. Researchers believe that this process could help people focus on specific behaviors or activities — in this case, taking care of an infant. In other words, a “loss” of brain material might seem like a bad thing, but the changes could actually, in part, be beneficial to people faced with new conditions like parenthood, according to Dr. Hoekzema.

Catherine Monk, Ph.D., a professor of medical psychology at the NewYork-Presbyterian/ Columbia University Irving Medical Center, speculated that this pruning might even be the cause of “mommy brain.” In Dr. Hoekzema’s study, the images showed reductions in gray matter in the hippocampus, which is largely responsible for regulating memory. Instead of focusing on relatively inconsequential tidbits of information, like a movie title, your pregnant or new-mom brain may reallocate resources to the parts of the brain that control “theory of mind,” which allows you to figure out what someone else wants and needs. Dr. Hoekzema says these same areas of the brain also lit up when mothers looked at their infants, suggesting that synaptic pruning might even promote mother-baby bonding.

“I’ve never seen anything like these changes,” Dr. Hoekzema said, comparing her 2016 study to her past research. Importantly, her study showed that such brain changes were consistent across all new moms, even if they had different life experiences.

Dr. Hoekzema’s study was also a boon for women’s health researchers, especially those who study pregnancy and motherhood, because it proved what many had hypothesized for years: Pregnancy and new motherhood are formative for brain function.

“We’re beginning to see that at this time, during pregnancy and the postpartum period, the adult brain is at its most plastic,” said Jodi Pawluski, Ph.D., a research associate at the University of Rennes in France. “Plasticity” refers to the brain’s ability to reorganize itself.

In 2015, Dr. Pawluski published a review of the available research on the maternal brain in the journal “Hormones and Behavior,” which determined that while more studies still need to be conducted, focusing on the maternal brain could teach us more about behavioral flexibility in all mammals. Dr. Pawluski noted that these natural brain changes benefit women throughout motherhood, but they may also be advantageous later in life, when women need to take care of their grandchildren or assume other caretaking roles.

Dr. Pawluski’s own research has already started to build on Dr. Hoekzema’s: She found a decrease in the production of new neurons during late pregnancy and the postpartum period in the part of the brain that governs memory. In her current research, she also observed an increase in new connections in the brain in postpartum mice. “I like to think [that] all these brain changes lead to some sort of more efficient behavioral outcomes,” she said.

Dr. Hoekzema has also continued her focus on the maternal brain; she’s working to understand more about how gray matter loss corresponds to behaviors specific to motherhood.

“Of course these vast brain changes must have a functional impact, but what functions are indeed altered by these brain changes?” Dr. Hoekzema said. “And how do these relate to maladaptive changes such as the development of postpartum depression?”

Dr. Simone Vigod, M.D., a women’s health psychiatrist and chief of the department of psychiatry at Women’s College Hospital in Toronto, is also working on mapping the maternal brain. She said pregnant women and new mothers are difficult to recruit for studies, because of busy schedules and safety restrictions. Funding for women’s health research can also be tough to come by. But despite these challenges, Dr. Vigod is looking at ways to treat mood disorders during pregnancy without medication. Her hunch is that synaptic pruning and brain reorganization might be linked in some way to the depression and anxiety that women can experience during the postpartum period.

And while much more research is needed, there’s even emerging evidence to suggest that brain changes during new parenthood might not be specific to just mothers. Fathers — and even potentially adoptive parents, nurses in the NICU, nannies and grandparents — might experience shifts in brain function to make them more effective guardians once they begin caring for a child, said Helena Rutherford, Ph.D., a researcher at the Child Study Center at the Yale School of Medicine.

“To move forward, we need people to acknowledge the value and importance of the transition to parenthood,” Dr. Pawluski said, recalling her own experience with forgetfulness during pregnancy. The experience was unsettling, she said, and it reminded her that educating parents on the potential reasons for these deficits can be incredibly affirming during a challenging time.

The birth of a child affects parents in a phenomenal way, she said. “If I can give knowledge to other people about that, I think I’m doing my job.”

Jenni Gritters is a freelance journalist based in Seattle. She covers health, psychology and travel.