Pregnancy alters women’s brains to favor the bond with their babies

Having children changes your life and also your brain. A study published in the journal Nature Communications shows that the surge in hormones during pregnancy modifies the brain structure of pregnant women and predisposes them to certain behaviors, such as bonding with the fetus first and with the baby later, or even preparing the home for the arrival of the baby, a behavior that is observed in many animals.

The authors, led by Elseline Hoekzema from the Amsterdam University Medical Center in the Netherlands, followed 40 women before and during pregnancy and after delivery, to observe changes in their brains at these stages. During that time, through diagnostic imaging techniques, they observed an increase in the activity of the Default Mode Network, a set of interconnected brain regions, as well as a decrease in gray matter volume, an effect that had already been observed in pregnancy in previous studies. All these modifications are related to intense changes in hormonal levels, particularly with the estradiol peak that occurs in the third trimester.

Hoekzema acknowledges that it cannot be said with certainty that these results mean that the woman’s brain is reprogrammed to care for her baby. However, they have seen “that these changes in the brain are related to the physiological and neural responses of the mother to the children,” with aspects of her maternal behavior and with problems in mother-child relationships.

“Similar to other mammals, reproduction-related brain changes in humans may thus be involved in the stimulation of maternal behaviors such as peripartum preparatory and caregiving behaviors, and the suppression of negative reactions to the infant,” the study concludes.

On this last point, the researcher notes that rats tend to avoid or even reject their pups, but a hormonal treatment that mimics pregnancy can produce maternal behavior in these females, reducing their negative reaction towards them and producing a sensation of great reward.

The authors consider it unlikely that factors such as the awareness of being pregnant or other psychological aspects could explain the large changes in the structure and function of the brain that they have observed. “No associations were found with other factors such as osmotic effects, stress and sleep,” notes Hoekzema, adding that although it is difficult to separate physiological factors from psychological ones, biological aspects of pregnancy likely represent the strongest factors that trigger these changes.

Although the effect of motherhood on animal behavior has been studied since the early 20th century, work to understand what happens in the brain of pregnant women is recent. In 2016, Hoekzema published a paper in Nature Neuroscience that pointed out the changes in brain structure experienced by pregnant women. Among other things, the study showed a reduction in the volume of gray matter. This process, which has also been seen in adolescence, could be a way of eliminating some brain connections to facilitate the creation of new ones, in this case, those necessary to take care of the baby.

That earlier study, supervised by Susanna Carmona from Gregorio Marañón Hospital in Madrid and Oscar Vilarroya, from the Autonomous University of Barcelona, opened up this new area of research. These two researchers are now at the head of BeMother, a project funded with €2.5 million by the European Research Council to study these adaptations for motherhood during pregnancy and postpartum.

The goal of this line of research is, on one hand, to characterize this possibility of change that the brain shows during pregnancy. “Before, it was thought that neuroplasticity was limited to childhood and adolescence, but this line of research calls into question that it does not exist in adults,” explains Magdalena Martínez, a neuroscience researcher in the Neuromaternal group of the Health Research Institute of Gregorio Marañón Hospital and one of the coordinators of the BeMother project. Pregnant women’s brains change, firstly from exposure to a burst of hormones, but also from interaction with the baby after delivery. The second objective of this research is that “if we characterize how women adapt in a non-pathological way to these changes, then we could see what to do to help women who suffer from disorders such as postpartum depression, which affects 20% of mothers.”

The researcher has also looked at the effects of paternity in first-time fathers. “We analyzed two groups of fathers, one from California and one from Spain, and we saw brain changes, although not as pronounced as in the case of pregnant women,” recalls Martínez. In the fathers, they saw changes located in the cerebral cortex, the outer layer of neural tissue in the cerebrum, but in the women, in addition to changes in the cortex, they saw changes at the subcortical level, “in evolutionarily highly conserved regions, which we share with other animals and which are more basic,” says the researcher.

However, Martínez warns against drawing hasty conclusions and says it is necessary to continue investigating. In addition, “it is possible that this reward that is the baby, which makes you want to be close and take care of it because it produces pleasure, is more potentiated in the pregnant mother and that the man has to work on it a little more.”

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