“Baby brain” can begin in pregnancy, when the woman’s brain is rewired so that she can urgently respond to her baby’s every need.
It is difficult to study the effects of a surge in pregnancy hormones in women.
However, in pregnant mice, brain cells that were highly activated by these hormones were found to make them more interested in babies than in food, the opposite sex, or new experiences.
Interestingly, this effect wore off in mice about 30 days after birth.
If the same is true for women, as researchers expect, it would mean that they become slightly more interested in people other than their babies about a year into motherhood.
The results showed that there was no significant difference in memory, cognitive function, or mental processing speed between mothers and non-mothers
This is about the time when they may want to pay attention to their partner again if they want another child.
The study helps explain women’s “baby brain,” where they are hypersensitive to their baby’s crying and needs, but not baby brain – as the term is sometimes used – in the context of forgetfulness in motherhood.
The findings about the pregnant brain come from scientists studying the role of two hormones that rise sharply in pregnant women and mice – estrogen and progesterone.
The researchers found that these hormones likely caused mice to behave more maternally in late pregnancy.
When the hormones were blocked from reaching brain cells through genetic editing, the pregnant mice became far less interested in carrying, feeding, or keeping warm their babies.
The hormones were found to have an impact on a part of the brain called the medial preoptic area (MPOA), which is also found in women.
Brain monitoring then showed that this part of the brain was far more active when pregnant mice interacted with baby mice than in response to food, a male mouse, an object they had never seen before, or a female mouse.
Dr. Jonny Kohl, lead author of the study from the Francis Crick Institute in London, said: “We found that changes in the brain to prepare for caring for a child begin during pregnancy – rather than after birth.”
“This is probably why mothers are prepared for child care and are overly sensitive to a crying child – perhaps they initially prioritize their baby over other people.”
“Some of these changes we saw in the brain appear to be lifelong.”
The study, published in the journal Science, found that non-mother mice often ignore small baby mice – which researchers say is like non-parents being annoyed by crying babies on planes.
But pregnant mice were more likely to stay in the nest with their offspring, retrieve them when they left the nest, and crouch over them to keep them warm and fed—much like females who stayed close to and cared for their babies cared.
Hormones have been linked to these behaviors based on results when they were blocked from reaching brain cells.
Scientists also found that pregnant mice reacted on their mother’s side to pups they had only seen once – suggesting this was a behavior hardwired into the brain.
Estrogen was found to trigger greater activity in a specific group of brain cells in the MPOA called galanin-expressing neurons – which humans do not have.
These were more active, with brain activity evident when several pregnant mice were presented with a baby mouse compared to another adult, food or an object.
Brain cells remained more active just 30 days after birth, but the effects of progesterone, which apparently causes brain cells to communicate more, did not disappear either.
Researchers believe that these changes caused by progesterone, which make babies so important to their mothers, may last lifelong.