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Pregnancy causes visible changes in the female brain [bbc.com], enough to allow computers to determine whether a woman is pregnant by analyzing brain scan images:
Pregnancy reduces grey matter in specific parts of a woman's brain, helping her bond with her baby and prepare for the demands of motherhood. Scans of 25 first-time mums showed these structural brain changes lasted for at least two years after giving birth.
European researchers said the scale of brain changes during pregnancy were akin to those seen during adolescence. But they found no evidence of women's memory deteriorating. Many women have said they feel forgetful and emotional during pregnancy and put it down to "pregnancy" or "baby" brain - and, it seems, with good reason.
[...] This study, from researchers at the Universitat Autonoma de Barcelona and Leiden University and published in Nature Neuroscience [nature.com] [open, DOI: 10.1038/nn.4458] [DX [doi.org]], looked at the brain scans of women before they became pregnant, soon after they gave birth, and two years later, to see how the brain changed. And they compared these women's brains with those of 19 first-time fathers, 17 men without children and 20 women who had never given birth. The researchers found "substantial" reductions in the volume of grey matter in the brains of first-time mothers. The grey matter changes occurred in areas of the brain involved in social interactions used for attributing thoughts and feelings to other people - known as "theory-of-mind" tasks.
Also at NYT [nytimes.com].
Here's an unrelated study [jamanetwork.com] [open, DOI: 10.1001/jama.2016.17383] [DX [doi.org]] that found that self-reported cannabis use during pregnancy increased [livescience.com] from 2.37% to 3.85% between 2002 and 2014. Uses include the treatment of morning sickness [reuters.com].