Sophia Loren said that “When you are a mother, you are never really alone in your thoughts”. She was more right than she knew: a mother isn’t alone in her thoughts, because her child’s cells have quite literally taken up residence in the mother’s brain.
The umbilical cord is not a one-way street of nourishment flowing into a fetus; fetal cells flow back and find permanent homes, interloping amongst their more-mature maternal counterparts.
When I told my sister – whose son is about to turn four – about these cells, she immediately dubbed them “cootie cells”, and had an immediate question:
Are those the cells that now find farts and fake puking hilarious?
Alas, we are a long way from knowing what precisely these microchimeric (or cootie) cells do. We only know for sure that this happens there is no other reason for Y chromosomes to be found in a woman’s brain; determining function is much more complicated than identifying an out-of-place sex chromosome. Even then, the current focus of fetal microchimerism research seems to be on health benefits such as repair to damaged organs and health risks such as autoimmune disorders. The fetal cells that make their way to the brain are certainly forming connections there, but whether those connections are involved in emotional reactions linked to disgust and humor is yet to be determined.
Cooties cells are just one way that the maternal brain changes in pregnancy and childrearing, of course. The “love drug” oxytocin is very popular, although probably widely misunderstood. Perpetual sleep deprivation will leave its own mark as well. But for mothers in search of an explanation for their minds seeming to go off into alien territory, cellular invasion may be the new best thing.