Neuroscientists have identified “selective and robust” changes in neural architecture and neural network organisation during pregnancy that appear to be linked to maternal behaviour.
While the findings are purely correlational, the changes may contribute to behaviours such as mum-bub bonding, nesting and physiological responses to cues from the baby, the researchers say.
The international team followed 40 women before, during, and after pregnancy and then one year post-partum, plus a control group of the same size who did not become pregnant during the study.
Regular scans were performed including MRI, diffusion weighted imaging, 1H-nuclear magnetic resonance spectroscopy and resting state functional MRI acquisitions to comprehensively investigate the impact of pregnancy on the human brain.
At the same time, they acquired profiles of their subjects’ hormonal changes based on biological samples collected every four weeks, in combination with factors like sleep and stress.
A key finding was functional connectivity increased during pregnancy in the Default Mode Network (DMN) – the group of interconnected brain regions that are most active when the mother is at rest – which returned to baseline levels a year after the birth of the child.
Additionally, the authors found an association between DMN functional activity during pregnancy and measures of mother-infant bonding in the late post-partum stage.
They also confirmed previously observed changes in the grey matter volume of the DMN during pregnancy.
These changes were correlated with pregnancy hormone levels, primarily third-trimester oestradiol, while no associations were found with other factors such as stress and sleep.
Alterations in white matter structure were not observed during pregnancy.
Writing in Nature Communications (link here), the team led by Dr Elseline Hoeksma of the Brain and Development Research Center, Leiden University, Netherlands, noted pregnancy represented a “monumental transition and one of the most extreme endocrine events of life”.
Even more subtle changes in sex steroid hormone levels were known to impact brain structure in function, the authors pointed out.
“The endocrine climate of pregnancy thus represents a likely candidate for anatomically shaping the female brain during this transitional period,” they wrote.
“The observed findings suggest that especially the unparalleled oestrogen exposure in the final stages of pregnancy may play a primary role in the induction of pregnancy-related structural neuroplasticity.”
Interestingly, associations were also observed between the neural changes across pregnancy and the subsequent development of mother-infant bonding across the postpartum period, including correlations with further changes in measures of infant-directed hostility and the pleasure experienced by the mother in the interaction with her infant.
“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 wrote.
They added that the changes related to measures of maternal-fetal bonding, nesting behaviour and the physiological responsiveness to infant cues, and predicted measures of mother-infant bonding and bonding impairments.
“These findings suggest there are selective pregnancy-related modifications in brain structure and function that may facilitate peripartum maternal processes of key relevance to the mother-infant dyad,” they wrote.