The maternal brain, another territory until now forgotten by science

Being a woman and a biologist, that is to say, having studied the life sciences, I am still surprised by how little I know about the biological changes that being a woman entails. Conversing with friends, we comment that no one ever explained to us what menopause really involved, as well as the associated bodily, organic, and metabolic changes. Regarding menstruation, although it may seem that it is now liberated and that everyone talks about it freely, it is also not explained what it really means for a girl's body, nor the transient and permanent changes that this biological stage implies. Dysfunctions such as endometriosis are now starting to be diagnosed and studied; regarding the effect of contraceptive hormones on our body, they have only been mentioned to us for their contraceptive effect, but not for the extent of the unnatural hormonal treatment that it represents when taken prolonged over years; nor has anyone spoken to us about the loss of ovarian reserve with age, a matter that is now increasingly present because women want to be mothers at more advanced ages. It almost seems as if women were invisible.

Perhaps, then, it should not surprise us that we are not told about the numerous and very important alterations that pregnancy causes in a woman's body, not only regarding the visible changes in the uterus, abdomen, and body fat, but also in the brain, profound changes in "circuitry": the brain of the pregnant mother changes a lot, and we still do not know the extent of it. We are about to reach Mars and we are capable of generating artificial intelligence algorithms, but it turns out that we still do not know half of the population. We women are still a great mystery to be studied, because it goes without saying that we are not the same as men, who have always been the focus of the majority of biomedical research.

That sort of morning fog, sudden mood swings, momentary memory loss, an increase in sensory sensitivity, cravings, or a feeling of confused well-being. All of this that the rest of people look at with condescension, as changes caused by hormonal alterations, goes much further, and are in reality the symptoms of a dramatic remodeling of the connections in the maternal brain to adapt to pregnancy and motherhood, in order to generate a bond of union and a feeling of recognition and care towards the child, which will result in a higher probability of survival for the offspring.

These changes are biologically programmed, yes, and are the result of a complex hormonal, metabolic, and immune cocktail and of interaction with the placenta and the embryo, first, and with the baby, after birth, but at the same time they demonstrate that the brain is plastic also in adulthood. What is important is that these changes take place during pregnancy but persist years after birth. The woman's brain changes during pregnancy and motherhood, and the science that studies it, a new field of neuroscience, is called neuromaternal science.

The pregnant mother's brain changes in volume and connectivity – new ones are created and others are undone –. Experimental studies have been conducted on mouse and female rat brains after gestation that demonstrate these changes in detail, but, of course, the rodent brain is not equivalent to that of humans. What has been observed in humans? That there is a decrease in gray matter and an increase in white matter, in addition to other neurological alterations.

Although the studies are more limited and descriptive, a magnetic resonance analysis comparing the brains of more than 100 mothers after a first, second, or multiple pregnancies also shows differential changes depending on the number of pregnancies. In the first pregnancy, changes are observed in the frontotemporal area of the brain, in regions involved in memory and language processing speed, as well as in areas of the amygdala and hippocampus, which govern social bonding.

In the second pregnancy, these areas, already modified in the first, do not change significantly, but instead, the connectivity of sensorimotor regions, response to multiple stimuli, control of various tasks, and dorsal attention is modified more, changes very likely related to controlling several children at once. In mothers who have gone through multiple pregnancies, more diffuse changes are observed in the white and gray matter, which would imply a decrease in amyloid plaques and, overall, a certain rejuvenation of biological age compared to the brains of women who have not had any children or have only had one. All of this indicates that there are significant neurological changes associated with gestation and also during the postpartum period. Obviously, these changes in the structure and connectivity of certain parts of the brain, specifically in the regions of the hippocampus and amygdala, may explain why some women suffer from postpartum depression.

On the other hand, the placenta, the organ created by the embryo to feed and interact with the mother, is not airtight. Cells from the mother pass and incorporate into the embryo, but cells from the embryo also circulate to the mother (which is why genetic analyses can be performed from the mother's blood) and, furthermore, they settle within some organs, specifically within the brain. The pregnant mother has a chimeric brain with her own cells but also some cells from her embryo, a phenomenon called microchimerism. The mother retains a footprint of each of her children that can last for decades, and we do not know what impact it will have on the mother's health over time.

At least it seems that the fact of gestating multiple children provides a lower risk of neurodegenerative diseases, but it is still too early to make extrapolations in humans in the very long term. It is necessary to study in greater depth what these changes in the mothers' brains are according to the different stages of life. Neuromaternal science deserves, therefore, all the attention that until recently had not been given to it.