New mothers may experience forgetful moments, but their brains actually grow after giving birth, a US study has found.
Researchers at Yale University and the University of Michigan took brain scans of 19 women's brains two to four weeks after giving birth and again three to four months later. Each mother was also interviewed on both occasions about her experiences as a parent.
The results of the study show part of each mother's brain grew considerably between the first and the second brain scans. The structural changes occurred mainly in the prefrontal cortex, parietal lobes and the midbrain.
In animals, these areas are commonly activated by maternal behaviour. The study findings suggested changes in these brain regions may also be important to promote sensitive maternal behaviours in human mothers, said the researchers.
Mothers who gushed over their babies and reported more positive thoughts showed the greatest brain growth during the study period.
This postpartum period marked a critical time for the development of sensitive mothering, the study authors said.
Lesions to certain areas of brain have been linked to impaired maternal motivation and increased the likelihood of infanticide in animal mothers.
The lead researcher, Pilyoung Kim, said research in rodents had also found a mother's memory, particularly spatial memory, including where she can find food, improved after the birth of her young.
However, changes in mothers' brains occurred only when they interacted with their pups. When mothers just observed their offspring, the brain did not change, said Dr Kim.
The animal studies and Dr Kim's findings suggest maternal instincts may not be hard-wired in the brain, but grow as a result of a mother interacting with her newborn.
Despite past research in humans suggesting that up to 80 per cent of new mothers can suffer memory loss, often referred to as ''baby brain'', for up to 12 months after giving birth, the findings suggest infant-related memory may improve during these early months of parenthood.
''Mothers may feel more forgetful regarding things which are not baby-related, considering all the demands and changes they experience in their life during the first few months postpartum,'' said Dr Kim, whose findings are published in the journal Behavioural Neuroscience.