Pregnancy changes a woman's brain, altering the size and structure of areas involved in understanding the feelings and perspectives of others, according to a first-of-its-kind study.
Most of these changes remain two years after giving birth, at least into the babies' toddler years.
And the bigger the brain changes, the higher mothers scored on a measure of emotional attachment to their babies.
In the study, researchers scanned the brains of women who had never conceived before, and again after they gave birth for the first time. The results were remarkable: loss of gray matter in several brain areas involved in a process called social cognition or "theory of mind", which is the ability to register and consider how other people perceive things.
"We certainly don't want to put a message out there on the lines of 'pregnancy makes you lose your brain,' as we don't believe this is the case," said Elseline Hoekzema, a researcher who led the study at the Universitat Autonoma de Barcelona in Spain.
"Gray matter volume loss does not necessarily represent a bad thing," she said. "It can also represent a beneficial process of maturation or specialisation."
Pregnancy, she explained, may help a woman's brain specialise in "a mother's ability to recognise the needs of her infant, to recognise social threats or to promote mother-infant bonding".
The study, which took more than five years, involved women in their 30s who had never been pregnant but were hoping to conceive. Their brains were scanned before becoming pregnant and within few months after giving birth. For comparison, 20 women who had never been pregnant were also scanned twice, about the same number of months apart.
Only the pregnant women showed gray matter reduction, thinning and changes in the surface area of the cortex in areas related to social cognition. Changes were so clear that imaging results alone could indicate which women had been pregnant.
The researchers also scanned the brains of 17 men who were not fathers and 19 first-time fathers before and after their partners' pregnancies. The two male groups showed no difference in brain volume.
Researchers wanted to see if the women's brain changes affected anything related to mothering. They found that relevant brain regions in mothers showed more activity when women looked at photos of their own babies than with photos of other children.
Six months after giving birth, the mothers answered questions on the Maternal Postnatal Attachment Scale, used to assess a woman's emotional attachment, pleasure and hostility toward her baby. Mothers whose brains lost more gray matter volume showed less hostility and more attachment, Hoekzema said.
Experts said more research was required, involving more women and clearer assessments of social cognition to substantiate whether gray matter loss is truly linked to "theory of mind" and improved mothering skills.
New York Times