Two and half years ago, as I was getting ready for labor, I asked my attending nurse how long she thought it would take for the baby to finally make an appearance. She said she has seen a baby pop out in 20 mins or sometimes take 3 hours or more! I had hoped and prayed that I would be the 20 min lucky mom. After 3 hours of pushing and finally going through an emergency caesarian section, the upper limit of my nurse’s experience turned out to be mine as well. I was relieved, physically drained and thought is there any part of my body that is not bloated beyond recognition now? So when I recently read an article in the Science magazine about a new paper that for the first time shows how women’s gray matter is significantly reduced after pregnancy (1), I was very intrigued.
The authors preface this study by sharing that other studies have already shown that significant physiological changes in the female brain result from changes in the sex steroid hormone levels upon attaining puberty. The focus of this study is the second time such hormonal changes occur in a woman – Pregnancy. What they measure here is Gray Matter (GM) volume using a Magnetic Resonance Image (MRI) scanner. So what is gray matter? Very simply, it includes various types of cells and cell bodies that make sure the brain is able to function well. Basically they are measuring any changes in the density of cells in the various regions of the cerebral cortex of the brain (see Fig.1).
In 25 first time mothers they tested, they saw a significant reduction in GM volume post pregnancy compared to their pre pregnancy measurements, and that of women who never became pregnant during the course of this study (5.25 yrs). Their study included women who naturally conceived as well as those that underwent fertility treatment to become pregnant. The GM volume changes however were consistent among the women who became pregnant, no matter the method of conception. The consistency in GM volume reduction was so high (95%) that they claim they could predict whether a women had undergone pregnancy or not between MRI sessions just by observing that measurement alone. Interestingly, changes in GM volume were only seen in the mothers and not their spouses. So even though fathers have the knowledge of an upcoming child, their brain does not undergo the same physical changes. As mentioned above, GM consists of various different types of cells that perform different functions and as the authors point out, MRI data cannot provide information on which constituents of gray matter are undergoing a reduction as a result of pregnancy.
So what if the GM volume decreases? The areas in which they saw a decrease in GM volume overlapped with the same areas that fired when tasks defined as “theory of mind tasks” are performed (as defined by two other independent studies). Theory of mind tasks include a whole array of tasks that require the brain to assess the mental states of other people (2). In this study, the subjects were asked to look at their baby’s picture and a picture of an unrelated baby, and the areas that fired were within the regions that showed GM volume reduction, especially when the mother looked at pictures of her own baby. They also made mothers fill out Maternal Attachment Scale questionnaires for the first 6 months after birth and found that they could closely predict the quality of attachment between mom and baby based on the reduction in GM volume. Overall, they suggest that their experiments provide a peak into how the mom’s brain is altered possibly in preparation for motherhood and better interaction with her baby.
Mothers often joke that one of the side effects of childbirth is a reduction in memory. Going back to my job as a post-doctoral researcher was therapeutic for me and I felt that my mind worked more efficiently. In this study the moms were made to take various cognitive tests and to my relief, the authors found no significant change in the moms’ performance on the memory tests before and after pregnancy 🙂 . So ladies, yes our brains change but according to this paper, most likely to prepare better for our role as mothers and not to make us forgetful and absent minded!
Changes in the GM volume in almost all of the regions persisted two years after the birth of the baby in the mothers they were able to follow up with. Although there were no further reductions or increases in these areas, this was an interesting finding that these changes sustain long after birth of a baby. Some of the mothers that participated in this study had another child within the two years of their last MRI session. Although they did not participate in the follow up session, it would have been interesting to see if the GM volume changes were any different in these mothers.
From the results observed in the fathers who participated in this study, it might seem that the brain transformations are dependent on the biological hormonal changes associated with pregnancy. But what kind of changes occur in adoptive mothers? This paper does not touch on that. Since menopause is the third time that a woman’s body is subjected to big hormonal changes, it would be very interesting to learn more about how and if brain undergoes another physical transformation in preparation for that phase of life.
- Pregnancy leads to long-lasting changes in human brain structure (http://www.nature.com/neuro/journal/vaop/ncurrent/full/nn.4458.html)
- Fractionating theory of mind: A meta-analysis of functional brain imaging studies – (http://www.sciencedirect.com/science/article/pii/S0149763414000128)