Krystal Chen

A study published in the journal “Nature Neuroscience” found that, over the course of a pregnancy, women undergo structural and functional alterations orchestrated by endocrine fluctuations — an unparalleled surge of sex steroid hormones. The changes, primarily being a asymmetrical pattern of volume reduction in extensive gray matter (GM), endure for over two years within the postpartum period in areas except for the left hippocampal cluster.

Interestingly, the study, titled “Pregnancy leads to long-lasting changes in human brain structure,” found that the substantial reduction in GM volume, instead of being distributed randomly across the brain, is located in the association areas of the cerebral cortex: the area of the brain involved in social interactions used for attributing thoughts and feelings to other people — known as “theory-of-mind” tasks. Those selective reductions boost their process of social information, which prepares soon-to-be mothers with advantages in various ways, such as to help them recognize the needs of their child, be more aware of potential social threats, and be more attached to their baby.

During pregnancy, gray matter volume — a major component of the central nervous system — is influenced by the fluctuation of sex steroid hormones. Melissa Healy, a health and science reporter with the LA Times writing from the Washington, D.C. area, wrote “what set the pregnant women apart, then, was likely the storm of pregnancy-induced hormonal changes they were experiencing.”

Multiple scientific studies were conducted to confirm the results on the effect of a pregnancy on the human brain. Scientists performed a prospective neuroimaging study to observe detailed structural changes within subjects’ brains. They took images of the brains of primiparous (first-time) mothers and nulliparas to investigate the pregnancy’s effect.

Also, for eliminating confounding variables — such as the connection of brain changes to experience-dependent changes associated with approaching parenthood — scientists observed GM alternations of primiparous fathers across parent pregnancy. The “Nature Neuroscience” study stated “there were no changes in neural GM volumes in the fathers in comparison to the control group across this time period; the observed brain changes were selective for the women undergoing pregnancy between the brain scans.”

Studies showed that the pregnancy will only post significant biological changes on women — mainly through a reduction of GM volume. Using longitudinal and cross-section analysis, scientists detected that the cortical thickness and its surface area, structural properties of the cortical mantle which both contribute to cortical volume, tend to shrink over the period of the pregnancy.

Moreover, the reduction, instead of being randomly distributed, is selectively located within certain areas related to social cognition. “A visual inspection of the observed GM volume changes suggested a strong similarity to the theory-of-mind network,” the study said.

Brain-structural changes prepare women to face their upcoming newborns. No evidence of deteriorating memory has been found in pregnant women, but a statistically strong overlap of reduced structural results with the theory-of-mind networking brain area suggests that changes in GM volume across a pregnancy significantly predicts maternal attachment. After comparing neural activity on an fMRI task with multiple baby pictures involving women’s own infants and others, the quantitative result indicated that “nearly 30% of the voxels that responded more to the mothers’ own infants than to other infants were located in GM tissues that lost volume across pregnancy.”

Alternations in these mothers’ brains and behaviors require a long-term restoration. After comparing the brain structures of women who had been pregnant over two years ago to those with the pre-pregnancy baseline, scientists proclaimed that, except for the left hippocampal cluster, all the GM volume reduction tended to endure for over two years.

The scale of brain changes during pregnancy were akin to those seen during female adolescence, but a woman’s brain structures change dramatically across pregnancy through GM reduction. So, just by analyzing the brain images, computers were able to pick out the women who had been pregnant. The alternation, which mainly facilitates a mother’s social recognition skills, generally lasts for over two years.