Pregnancy caused long-term changes in brain structure
A group of researchers from Spain and the Netherlands have shown that pregnancy causes changes in the structure of the gray matter of the brain, continuing for at least two years after childbirth. The article was published in the journal Nature Neuroscience, and briefly about it it is told in editorial material of the journal Science.
During pregnancy the levels of sex steroid hormones varies greatly: for example, the amount of estrogen produced during pregnancy, usually exceeds the total amount of estrogen produced in a woman’s body for all the other periods of her life.
While in previous studies it has been shown that changing levels of sex steroid hormones can cause structural and functional changes in the nervous tissue of the brain. For example, in puberty the production of sex hormones causes large-scale reorganization of the brain, and in adults the change in the level of steroid hormones leads to neural alterations. Not surprisingly, in rodents and other animals pregnancy, as studies have shown, causes changes in nervous tissue on several levels, including changes in the morphology of dendrites, the intensity of the division of neurons and gene expression. In humans, however, systematic studies of this sort almost never undertaken. It is only known that in the later stages of pregnancy increases the size of the pituitary gland and decreases the total brain volume.
The authors of the new article used magnetic resonance imaging to track changes in the structure of the gray matter of the brain in 25 women, pregnant for the first time. Their brains scanned before and after pregnancy (after different time intervals from three weeks to several months). The analysis included 20 nulliparous non-pregnant women, and to eliminate the influence of parenthood (and not specifically pregnancy), 19 men, who are fathers, and 17 men without children. For all of these groups underwent brain scans with the same time intervals as for the test group of pregnant women.
It turned out that all mothers have experienced very similar changes in the volume of gray matter of the brain — so similar that all surveyed women could be easily categorized as parous and nulliparous solely on the results of scanning their brain. Most changes were concentrated in areas of the brain responsible for social skills — such as understanding emotions and intentions of other people by their faces and actions.
Also, the volume decreased hippocampus — the brain region that plays a key role in memory formation. None of the control group such changes were not observed. However, the decreasing volume of the hippocampus did not affect the memory of the postnatal period: a task for memory they didn’t get worse than before pregnancy. The only thing that managed to notice the researchers, is a small deterioration in verbal memory (however, the level differences were statistically significant).
Measuring using standard test force attachment of mothers to their children, the researchers also found that the strength of attachment is correlated with how much a woman’s brain has changed during pregnancy: the greater these changes, the greater was the attachment. Scientists have traced how the brain reacts to women on photos of their own children and photographs of other people’s children (how much different is the reaction of the brain to these stimuli, is also a measure of the strength of attachment). It turned out that about 30 percent of those brain regions that are selectively activated in response to pictures of their own (not others’) children, coincide with the areas of the brain, changed the amount during pregnancy.
Two years after these studies, 11 of the 25 mothers — those who in the meantime got pregnant again — again underwent magnetic resonance brain scans. It turned out that these women have still reduced the volume of gray matter in those same areas of the brain except the hippocampus, which returned to its original state. Surviving the changes were enough for only them to determine woman pregnant in the past or not.
What are the reasons for reduction in the volume of gray matter — a change in the number of synapses or neurons, with the restructuring of dendritic structure or with a change in the blood supply to the brain is still unclear. As the authors note, reducing the volume of gray matter observed in puberty, is associated (at least partly) with the so-called synaptic pruning: a reduction in the number of synapses to eliminate redundant connections and improve the efficiency of the neural networks. It is possible that similar processes occur during pregnancy, increasing the efficiency and SPECIALIZIROVANNOE work separate parts of the brain. In some studies, for example, it has been shown that in pregnant women improving the ability to recognize faces and emotions. The authors suggest that this may be associated with the parts of the brain responsible for social skills that they observed in their study.