How pregnancy changes a mom's brain
Posted January 4
It's not just a woman's shape that changes during pregnancy. Having a baby also affects a new mother's brain, and the changes linger at least until the child is a toddler, a new report says.
The changes occur in what's known as "gray matter," which makes up 40 percent of the brain and houses the cell structures of neurons. Portions of gray matter shrink noticeably after a woman gives birth for the first time, researchers said in the Dec. 19 edition of the journal Nature Neuroscience.
Legions of women who suffer bouts of forgetfulness after giving birth may say that explains a lot.
But the parts of the brain that are affected are the ones that govern what's known as "social cognition" or "theory of mind." These are the areas that allow us to empathize with others and to understand how their thinking differs from ours.
Rather than making new mothers less empathetic to their babies, however, the shrinkage may fine-tune the brain through a process called "pruning," the researchers speculate, noting that a similar process occurs in adolescence.
"Synaptic pruning in adolescence is generally regarded as an essential process of fine-tuning connections into functional networks and is thought to represent a refinement and specialization of brain circuitry, which is critical for healthy cognitive, emotional and social development," the authors wrote.
While damage or loss of gray matter has been associated with cognitive decline in Alzheimer's disease and multiple sclerosis, researchers believe the changes in new mothers work to make them more effective parents.
Reasons for the change
The research team at Autonomous University of Barcelona conducted brain scans of 25 women and 19 of their partners before they conceived, and then took follow-up scans two years after their babies were born.
They found that gray matter in the mothers' brains had declined measurably compared to their partners’ and to a control group of women who had not been pregnant. The change was so stark that the images alone revealed which women were mothers, The New York Times reported.
While many women complain of fuzzy thinking after pregnancy, the researchers said that a decline in gray matter doesn’t necessarily translate to a dip in brain function. In fact, the women in the study, who all lived in Spain, showed no change in memory or verbal skills, the Times' Pam Belluck reported.
The areas of the brain that showed change were the ones that govern social cognition. One of the authors said that the changes could mean that these regions of the brain were just working more efficiently after childbirth.
“Loss of volume does not necessarily translate to loss of function,” Elseline Hoekzema, a senior brain scientist at Leiden University in the Netherlands, told Susan Scutti of CNN.
And David Van Essen, co-principal investigator of the National Institutes of Health’s Human Connectome Project, said in CNN’s report that other factors could make it appear that gray matter had diminished, such as an increase in myelin, a coating that protects neurons.
Another possible explanation is that the changes are temporary and caused by external factors, such as post-pregnancy stress, diet and lack of sleep, neuroscientist Paul Thompson said in The New York Times.
Whatever the cause, the changes persisted even as the mothers' babies learned to walk and talk. The study ended when the children were 2, so it's unknown what happened after then, and what changes, if any, occurred in subsequent pregnancies. Similar studies of mice, however, have found that maternal brain changes can last for a lifetime.
The findings, which one doctor called “provocative,” seem to suggest that changes in the mother’s brain serve to increase her emotional connection to her child. The greater the change in gray matter, the more the women reported being attached to the child, the researchers said.
Although the new study was small and involved only well-educated women, it was apparently the first time researchers used brain imaging to examine women both before conception and after childbirth. And other doctors and researchers were intrigued by its findings. Ronald Dahl, a neuroscientist at the University of California, Berkeley, told Catherine Caruso, writing for Scientific American, that he had “a delightful ‘wow’ moment” when reading the study.
“This is a pioneering contribution that not only documents structural brain changes linked to pregnancy but also compellingly offers evidence that suggests these represent adaptive changes,” Dahl said.
The curse of 'momnesia'
Many women who have been pregnant don’t need research to confirm what they’ve already experienced. New mothers often report that their brains' way of processing the world at times seems as altered as their girth.
Call it gestational forgetfulness, "pregnancy brain" or "momnesia," it's an experience that is commonly shared on the internet. One California blogger, Maggie Downs, wrote on Babycentral.com that while she was pregnant, she once reported to work on a Sunday — her day off.
"What is it about having two brains in your body but feeling dumber than ever?" she wrote.
Previous research has confirmed that it's not all in their heads — or rather it is, but the phenomenon is real, not imagined. A survey of 14 studies conducted over 17 years found that pregnant women were "significantly impaired on some, but not all, measures of memory," and deficits in memory lasted throughout the postpartum period. Some researchers believe that fluctuations in hormones are to blame.
But don't discount the power of suggestion, another study says. It said that an expectation of pregnancy brain can lead to forgetfulness, or perception of forgetfulness. In other words, being pregnant can make you more likely to notice ordinary forgetfulness and to blame it on pregnancy.
Most likely, the brain also changes in ways that help ensure the baby's survival. As Adrienne LaFrance of The Atlantic reported last year, the areas that control empathy and social interaction are more active after childbirth. In fact, brain activity after childbirth is similar to that in people who are falling in love, LaFrance wrote.
Seeing your baby smile or hearing her cry lights up your brain in ways that exposure to another woman's child wouldn't. And being passionately in love with an infant makes middle-of-the-night feedings and diaper changes tolerable, if not pleasurable.
It may be more accurate to say that what goes on in a new mom's brain is "remodeling," not shrinking, Laura Sanders wrote on Sciencenews.org.
"Pregnancy (and possibly childbirth) may make these neural networks sleeker and stronger, helping moms to tune in to their infants," she wrote. And Sanders notes that research on the phenomenon has been "spotty," which suggests that more study is needed.
The study authors said additional research on changes in a new mother's brain could also help cast light on a problem that affects 1 in 6 mothers: postpartum depression. It could also answer questions the study raises, including whether the brain ever reverts to its original proportions, and if additional shrinkage occurs with each subsequent pregnancy, which remains unknown.