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‘Baby brain’ can begin during pregnancy, rewiring women’s brains so they can respond urgently to their baby’s needs.
It is difficult to investigate the effect of rising pregnancy hormones in women.
But in pregnant mice, it was found that brain cells powerfully activated by these hormones made them more interested in babies than in food, the opposite sex or new experiences.
Interestingly, this effect disappeared in mice about 30 days after delivery.
If the same is true for women, as researchers expect, this would amount to slightly more interest in other people 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 the mothers and non-mothers
That’s around the time they might want to pay attention to their partner again if they want to have another child.
The study helps explain women’s “baby brain,” where they are hyper-reactive to their baby’s crying and needs, but not baby brain — as the term is sometimes used — in relation to forgetfulness during motherhood.
The insight into the brains of pregnant women comes from scientists investigating the role of two hormones that increase sharply in pregnant women and mice: estrogen and progesterone.
Researchers found that these hormones likely caused mice to behave more maternally during late pregnancy.
When the hormones could no longer reach the brain cells through genetic engineering, the pregnant mice were much less interested in holding their babies, feeding them or keeping them warm.
The hormones were found to affect a part of the brain called the medial preoptic area (MPOA), which is also found in women.
Brain research then showed that this part of the brain was much 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, senior 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 – and not just after birth.
“This is probably why mothers are primed for childcare and hyperreactive to a crying child — perhaps prioritizing their baby over other people at first.”
“Some of these changes we saw in the brain appear to last a lifetime.”
The study, published in the journal Science, found that non-mother mice often ignore baby mice – which researchers say is similar to non-parents becoming irritated by crying babies on planes.
But pregnant mice were more likely to stay in the nest with their offspring, picking them up when they left and crouching over them to keep them warm and fed – just as women stay close to and care for their babies.
Hormones were linked to this behavior, based on the results when they could not reach the brain cells.
Scientists also found that pregnant mice responded maternally to pups they had seen only once – suggesting this was a hard-wired behavior in the brain.
Estrogen was found to cause more robust activity in a specific group of brain cells in the MPOA, neurons that express galanin, which humans do not have.
These were more active, as the brain activity showed, when several pregnant mice were presented with a baby mouse, compared to another adult, food or an object.
The brain cells remained more active for just 30 days after birth, but the effects of progesterone, which appears to help brain cells communicate better, did not disappear in the same way.
Researchers believe that these progesterone changes that make babies so important to their mothers could be lifelong.