Neuroplasticity of the maternal brain during pregnancy and postpartum

Feb 15, 2024 | Neuroscience (Featured)

The brain is an organ that adapts its anatomy and function during pregnancy. The specific changes in physiology and neuroplasticity of the maternal brain during pregnancy prepare the mother for the challenges of motherhood and contribute to the survival of the offspring. Numerous neuroimaging studies have investigated the changes in the maternal brain during pregnancy and lactation.

The first study: the changes in the organization of the neural network during pregnancy

The authors from the Netherlands used different types of neuroimaging, including magnetic resonance imaging (MRI), resting-state functional MRI (fMRI), diffusion-weighted imaging, and 1H-nuclear magnetic resonance spectroscopy to investigate the modifications in the organization of the neural network and the structure of white or gray matter in the human brain during pregnancy. 

This prospective cohort study included 40 pregnant women and 40 control nulliparous women. 28 pregnant women participated in the late postpartum assessment. The temporal coherence between and within neural networks was examined by comparing the brain scans of pregnant women with those of nulliparous women. The hormonal changes in the biological samples were assessed every four weeks during pregnancy. Women were followed from the preconception period to the late postpartum period.

The findings revealed a significant reduction in the volume of gray matter in pregnant women compared to nulliparous women. This reduction primarily affected the anterior and posterior cortical midline and specific sections of the bilateral lateral prefrontal and temporal cortex. The changes in gray matter volume correlated with myoinositol, the marker of glial cells, suggesting that the changes in gray matter volume at least partially reflect the changes in glial cells.

There were no significant changes in the white matter diffusion metrics or volume between the pregnant women and nulliparous women, despite the highly pronounced changes in the structure of the gray matter. Hence, the authors concluded that the structure of white matter in the maternal brain remains relatively stable throughout this period.

However, the results showed that pregnancy caused selective and robust changes in neural architecture and neural network organization, mainly pronounced in the Default Mode Network (DMN), a group of highly interconnected brain regions that are most active in the absence of a specific task. DMN reflects the brain’s baseline activity and is involved in autobiographical memory, self-perception, and social processes, like social cognition, social assessment, and empathy.

The resting state fMRI data demonstrated a selective increase in DMN coherence in pregnant women compared to the control group. This included an increase in DMN coherence in the cuneus, which plays a crucial role in visual processing and integration of visual information with working memory, attention, and reward expectations. According to the authors, pregnancy is associated with structural and functional plasticity within the DMN, indicating a change in the baseline activity of the maternal brain.

During the third trimester, the observed neural changes correlated with the levels of gonadal hormones, specifically with estradiol levels. The researchers suggested that marked changes in the gray matter structure, and insignificant changes in diffusion metrics or white matter volume, could be due to a particularly strong sensitivity of gray matter to fluctuations in gonadal hormones.

The scientists then investigated whether the neural changes observed during pregnancy remained persistent throughout the postpartum period. The results showed that modifications in the structure and plasticity of the maternal brain were partially reversed during the postpartum period. In addition, the duration of breastfeeding correlated positively with the extent to which the increased DMN coherence was restored in the postpartum period. This suggests that prolonged breastfeeding induces a sustained maintenance of neural changes observed in pregnancy.

According to the authors, these results showed marked and selective changes in the structural and functional plasticity of the maternal brain during pregnancy, which is crucial for the mother-infant dyad.

This article was published in Nature Communication.

Journal Reference

Hoekzema E. et al. Mapping the effects of pregnancy on resting state brain activity, white matter microstructure, neural metabolite concentrations and grey matter architecture. Nat Commun 13, 6931 (2022). (Open Access)

The second study: a decrease in cortical volume in the maternal brain during pregnancy was followed by an increase in cortical volume in the postpartum period

In this MRI study, the Spanish authors investigated the changes in the brain cortical structures during the peripartum period. They hypothesized that neuroplastic processes during pregnancy and the postpartum period would have the opposite effects on the cerebral cortex and that a decrease in cortical volume across multiple brain networks during pregnancy would follow an increase in cortical volume during the postpartum period.

110 first-time mothers aged 24–43 years were studied at the end of the third trimester of their first pregnancy and during the first month postpartum. A control group of 34 age-matched nulliparous women was assessed at the same time intervals.

The MRI findings demonstrated reductions in cortical volume present before childbirth. In late pregnancy, mothers had lower global cortical volume and thickness than controls across all functional networks. These differences were widespread and included midline regions from the medial prefrontal gyrus into the anterior and posterior cingulate, as well as the lateral areas, like the precentral and postcentral sulci, the dorsolateral prefrontal cortex, and the temporoparietal junction.

The authors stated that there is a broad consensus that reductions in cortical volume related to pregnancy are mostly confined to DMN, a key system for self-referential processing and social cognition (mentioned in the first study here), but their results demonstrated a significant reduction in other large functional brain networks during pregnancy.

In the early postpartum period, some changes observed during late pregnancy were attenuated but, mothers still had a lower cortical volume and thickness than controls. 

The increase in cortical volume that started in the early postpartum period was widespread, and primarily affected midline regions, like the posterior cingulate, the paracentral gyrus, and precuneus, and lateral regions, like the precentral and supramarginal gyri and the superior temporal gyrus. However, the increase in DMN volume and the fronto-parietal network was less than expected in the early postpartum period, suggesting their longer persistence. Indeed, reductions in DMN cortical volume were reported at one, two, or six years postpartum.

This study has shown that reductions in most networks adjust or recover during the early postpartum period, except for those affecting higher-order cognitive networks, such as DMN. These findings indicate that cortical reductions in the brain networks that occurred during pregnancy were attenuated in the postpartum period at a different rate.

This article was published in Nature Neuroscience.

Journal Reference

Paternina-Die M, Martínez-García M, Martín de Blas D. et al. Women’s neuroplasticity during gestation, childbirth and postpartum. Nat Neurosci 27, 319–327 (2024). (Open Access)

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