The mental fog that can come with pregnancy – commonly referred to as ‘baby brain’ – isn’t merely the result of discomfort, stress, and sleepless nights: A mother’s brain really does seem to change to accommodate the new arrival.
A new study by researchers from the Netherlands has uncovered strong evidence of a relationship between surges in pregnancy hormones and changes to the architecture in areas of the brain involved with contemplation and daydreaming.
Putting aside the forgetfulness and difficulty maintaining focus, the modifications could be nature’s way of helping mothers bond with their new bundle of joy.
Anecdotes of absent-mindedness during pregnancy are universal, informally described with terms like ‘mommy brain’ and ‘momnesia’. As common as the phenomenon seems, its subtle effects have been notoriously difficult to measure.
Leiden University neuroscientist Elseline Hoekzema has researched the neurological changes that come with human and animal gestation for several years.
A 2016 study led by Hoekzema showed how pregnancy coincided with significant reductions in gray matter, the tissue that carries messages and conducts the brain’s computations.
“During pregnancy, a woman is exposed to an unparalleled flood of hormones,” Hoekzema said in 2020, following a €1.5 million European Research Council grant for continuing research into pregnancy and neurological change.
“Animal studies have shown that these hormones trigger far-reaching changes in the maternal brain and behavior. In previous studies, we discovered that pregnancy renders long-lasting changes in human brain structure.”
For this latest study, Hoekzema and her colleagues mapped the brains of 40 mothers with MRI scans. They conducted the scans during pre-pregnancy and pre- and post-birth, including imaging a whole year after the baby’s delivery.
These scans were compared with similar images taken from a sample of 40 women who weren’t pregnant at the time of the study.
Hormones were tested through urine samples every two to four weeks throughout the test group’s pregnancy. The mothers’ attachments to their babies – nesting behaviors, sleep patterns, and levels of psychological distress – were analyzed through surveys and questionnaires.
Based on the results of the 28 volunteers who completed the study, pregnancy hormones don’t just tweak the brain’s ‘thinking’ cells: They appear to change the very way the brain networks together.
These changes are most pronounced between regions of the brain referred to collectively as the Default Mode Network, which activates when focusing shifts from the outside world to inner thoughts.
While it’s known that sex hormones like estrogen and testosterone strongly influence the pruning and shaping of our neurological gardens, this new study demonstrates precisely how fluctuating pregnancy hormones, such as estradiol, hold particularly strong sway over specific regions of the brain.
Just why a growing baby might want momma to become a little vague during pregnancy isn’t obvious. But the questionnaire results might provide something of a clue.
Responses from the new mothers suggested having baby brain might help with the bonding experience, facilitating behavioral changes that make those stressful months of adjusting to a newborn just a little easier.
“These findings suggest that the neural changes of pregnancy may render a blueprint that facilitates the subsequent development of the mother-infant relationship, which could then potentially be further reinforced by the interaction with the infant,” the authors write.
Demonstrating a clear cause-and-effect relationship in studies like these is challenging, making conclusions like these largely speculative. Further studies based on larger groups, perhaps with better analytical tools for diving deep into changes on a cellular level, might help support or refute the interpretations.
For now, we all need to be a little more forgiving of moms-to-be when they tune out of conversations or forget where they put their keys. It could be their brain making room for another tiny human to love.
This research was published in Nature Communications.