Their initial study, published in 2016, revealed for the first time that pregnancy produced significant structural changes in a woman’s brain that endured for at least two years after birth. Hoekzema’s colleagues now have a seven-year-long study that shows the same structural changes in different women. They also found that pregnancy alters the function a key brain network that is involved in self-reflection. According to the work, which appeared on November 22 in Nature Communications, the brain changes correlate with a mother’s enhanced bonding with her baby. These findings were derived by studying the physiology of female participants and using questionnaires to assess their mental and behavioral state. The researchers discovered strong evidence that female hormones were responsible for this phenomenon for the first time in humans.
The biggest changes are in a brain system that is active when the brain’s activity is idling –, that is, when it is not engaged with any task. This suggests that pregnancy alters the organs’ baseline state. Jodi Pawluski (a neuroscientist at University of Rennes 1 in France) said that the researchers are seeing functional connectivity changes even when the brain is at rest. She studies the maternal brain as well as perinatal mental illness, but was not part of the study. This speaks to the importance of this stage in a person’s life, and how it can be transformative in the brain
In 2015 Hoekzema and her colleagues recruited 89 young Dutch women who had never had a baby. After five years, 40 of them had a child, nine dropped out, and 40 served as controls. The women had brain scans to determine structure of their brain and the functioning of its networks before conception, shortly after birth and, for 28 of the mothers, more than a year after birth. A battery of tests were performed during this time, as well as in the third trimester. The hormone levels in the urine of pregnant women were tested every two to four week.
The investigation was “tremendous,” according to Joseph Lonstein, a neuroscientist from Michigan State University who studies maternal behavior in rodents, but was not involved in it. It has brain structure. It has brain function. It has steroid hormones. He says it has a woman’s attachment to their baby.” “It has women’s attachment to their infant,” he says.
The Dutch women who became pregnant showed the same structural brain changes as the pregnant women that Hoekzema and her colleagues examined in their smaller 2016 study. Both studies showed that gray matter, which is tissue located near the brain’s surface and made up mainly of neuron cell bodies and associated structures, was reduced in the women in both studies. Experts say that the tissue loss is not necessarily a bad thing. It could be due to brain remodelling similar to that which occurs in adolescence .. The new study’s replication of the 2016 results was “very important,” Lonstein says. “This just shows that some of these findings are robust enough that they will be found again and again,” Lonstein says. However, there were no differences in the underlying white matter of the pregnant women, which is composed of nerve fibers that transmit signals across the brain.
The researchers also used functional magnetic resonance imaging to analyze the activity within and between all the brain neural networks. They focused on “connectivity”, or the degree to which brain regions activate in unison. This is a measure of their strength. Pregnancy-related differences showed up in only one network, the default mode network, which is thought to govern self-reflection, as well as social processes such as thinking about others.
Connectivity within the network was higher in pregnant women. Connectivity within this network was greater in pregnant women. This is because she saw the fetus more as a person with her own needs. Hoekzema states that these changes in the default network could indicate that there has been some change in the neural representations of the self throughout pregnancy.
Brain modifications that help the mother to see the developing baby as an individual are likely play a role later in mother-baby bonding, Hoekzema states. The physiological measure of maternal-fetal bonding was also found to be related to connectivity in the default mode network. This included a slower heart rate when mothers see smiling infants. These are often rewarding for mothers. A woman’s heart rate slows when she has more connectivity. This is a reflection on how interesting and attractive the photos are to her.
Researchers also discovered that subtle changes in the default network could predict if a woman is likely to show signs or infant-directed anger. Hoekzema states that there could be a link between brain changes and the suppression of negative reactions in young children as well as the facilitation positive behaviors that help mothers.
Changes in gray matter with pregnancy were, again, most prominent in the default mode network. These changes were similar to “nesting” or preparatory behaviors such as cleaning the house that women display in late-term pregnancy, says Hoekzema who is now a mother to two.
Hoekzema also examined what factors might be responsible for brain remodeling. The team found no correlation with sleep, stress, or delivery method but did find a strong association with rising estrogen levels. This finding makes sense because changes in sex steroid hormones are known to reconstruct areas of the female rodent brain and are responsible for maternal rodent behaviors such as nest building and caring for pups. Pawluski states that it is important to show that what is true in animals can also be true in humans.
Pregnancy-related gray matter loss generally persisted a year after giving birth, the researchers found. The exception was the hippocampus. This memory structure’s gray matter had a tendency to increase in volume over this time, which parallels a cognitive recovery that studies show takes place over two years. So the real “mommy brain,” Hoekzema says, may be largely supercharged for parenting but at a temporary cognitive cost, something she plans to more fully investigate in a future study.
Pawluski is both a scientist and a therapist. She believes that mothers who become mothers can find comfort in the fact that their brains have changed. This allows them to accept different emotions or psychological shifts. And the results may ultimately inform situations in which motherhood goes awry because of depression or psychosis, potentially leading to new diagnostics. Pawluski states that if you could determine from a brain scan or a biomarker in blood whether someone is at risk for a perinatal mental disorder, that could prove very valuable.