Introduction
I would like to discuss a study in Nature Neuroscience by Hoekzema et al that I came across yesterday which seems to suggest some fascinating conclusions regarding a phenomenon know as "pregnancy brain".
I would like to present and discuss some of the main findings of this study and will endeavour to keep it brief.
If you are interested in the subject I would definitely recommend reading the paper which is available in full here:
http://www.nature.com/neuro/journal/vaop/ncurrent/full/nn.4458.html
Most people know that pregnancy induces substantial mental and physical changes in women. This new study suggests that pregnancy may also lead to structural brain changes.
Study Design
This was a prospective study which looked at women who had not previously given birth and were wanting to get pregnant.
The researchers then performed MRI scans before the women became pregnant and then followed up with further scans after their pregnancies were completed. These were then compared with control women who had not given birth and also compared with their pre-pregnancy scans.
There was also a comparison made with males who became parents pre and post pregnancy to see if any changes might actually be related to becoming a parent rather than pregnancy itself.
The final samples consisted of 25 primiparous (first time birth) women and 20 nulliparous (never given birth) control subjects.
Results
The volumes of Grey Matter showed statistically significant reductions in women after pregnancy compared to their pre-pregnancy scans and the control subjects.
The main areas involved were located in the anterior and posterior mid-line as illustrated in this beautiful graphic:
It is beyond the scope of this post to go into the detailed discussion of the specific neuroanatomy but the areas involved have been associated with social function.
The regions of GM change affected by pregnancy are known to play a role in social cognition, and a visual inspection of the observed GM volume changes suggested a strong similarity to the theory-of-mind network.
Although a reduction in grey matter may initially seem like a bad thing it may actually indicate an enhancement in brain function as a result of a process called pruning.
This is a process that occurs throughout childhood brain development and during adolescence. This is a streamlining process where un-necessary cells and connections are removed, resulting in faster and more efficient processing.
One analogy that I found useful to think of concerning pruning is imagining it to be like the etching of a silicon circuit board. Material may be lost but the actual end result is more capable and effective at a particular function than what you started with.
Cognitive Testing
Consistent with the "pruning" hypothesis there were no significant changes in the majority of cognitive tests performed:
We conducted several cognitive tests at the sessions before and after pregnancy. A verbal word list task was used to examine verbal memory, and changes in working memory were investigated using a backward digit span task and a two-back test. No significant changes were observed across sessions in these measures in comparison to the control group, although a trend was observed for a reduction in the number of correct responses on the verbal word list learning task
The one area of reduction is of interest although I wasn't able to find the raw data pertaining to this. It may indicate a change to working memory but I would need further information to comment properly. The way it is stated does not suggest that it is anything significant and it may be that follow up studies reveal this to be an anomaly.
Other points of interest
The researchers did a lot of different tests and there is a wealth of data in this paper which is really too much too cover in a post of this sort. There were some other things that stood out to me:
- Maternal attachment scale scores were strongly associated with the changes in GM volume. To put it simply the greater the changes the greater the attachment between mother and infant.
- Long term follow up (e.g. 2 years) in 11 of the women showed the changes were mostly enduring.
- No similar effects were seen in males who became first time parents.
Potential Problems
Having peripherally taken part in studies of this sort at University I understand a lot of the problems that they have. Most of these relate to the large costs, time and immense amounts of data involved.
These all confer certain limitations:
- Sample sizes were quite small (i.e. 25 subjects vs 20 controls) - by the nature of such a study it is incredibly expensive and time intensive so this is understandable.
- Recruitment was via one specific location in Barcelona. Is this a location specific effect, e.g. one population group, something environmental etc.?
- 16 of the 25 women underwent fertility treatment to become pregnant - does the fertility treatment itself lead to an exaggerated or spurious result? The paper takes this into consideration and it seems that the changes are quite consistent across these subgroups.
- Are the changes related to pregnancy itself or due to some other intervention that occurs in pregnancy - e.g. related conditions, type of delivery, anaesthesia etc.?
- Is there another confounding factor like pre-existing mental illness which may alter GM volume?
- Is the reduction in one of the cognitive tests an anomalous finding in this particular study?
To be fair the study does take most of these factors into consideration, through testing, exclusion criteria and further data analysis.
You can see how they do this in the Methods section if you would like to make your mind up about how effective they are.
I think they do a decent job overall although no study is perfect.
I think the most important thing (as always) is to see if these results can be duplicated in further studies done at different times and in different locations. It would also be interesting to look at the effect of subsequent pregnancies on brain volume - does this lead to further changes?
Conclusion
This is a very interesting study which suggests that women's brains may undergo remodelling in specific regions related to socialisation during their first pregnancy.
This has some parallels to the brain pruning that occurs during adolescence and appears to be consistent with enhancement of social functioning in areas related to maternal-infant attachment.
This gives strength to the idea of "Pregnancy Brain". As always further research is needed to confirm and strengthen the validity of these findings. It would also be interesting to study the effects of subsequent pregnancies on the maternal brain.
I hope I have struck the right balance between brevity and avoiding rehashing too much of the original article. Please let me know what you think in the comments.
Reference:
Hoekzema, Elseline, Erika Barba-Müller, Cristina Pozzobon, Marisol Picado, Florencio Lucco, David García-García, Juan Carlos Soliva, et al. 2016. “Pregnancy Leads to Long-Lasting Changes in Human Brain Structure.” Nature Neuroscience, December. doi:10.1038/nn.4458.
Online link: http://www.nature.com/neuro/journal/vaop/ncurrent/full/nn.4458.html
Thank you for reading.
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