Summary: Researchers have delved into the neurobiological evolution during pregnancy and postpartum, shining a light on brain changes and maternal behavior. Hormonal fluctuations, especially related to estrogens, are believed to induce brain plasticity during these periods.
This study builds on a 2017 revelation that pregnancy causes shifts in a mother’s brain morphology. However, understanding the complex dance of hormones, brain adaptations, and subsequent maternal behavior still requires more exploration.
- Pregnancy induces changes in a mother’s brain morphology, specifically a reduction in gray matter in regions linked to social relations, which lasts for at least two years post-birth.
- Estrogens are considered the principal hormones responsible for inducing these brain changes.
- The emotional and cognitive processes that form the evolving mother-child relationship, particularly during pregnancy and postpartum, remain one of the least understood areas and distinguishes human mothers from other animals.
Researchers from the Universitat Autònoma de Barcelona (UAB), the Gregorio Marañón Health Research Institute and the Hospital del Mar Research Institute have published the first paper that reviews the scientific literature on the neurobiological adaptation occurring during pregnancy and postpartum in humans and other animals.
The article, with Camila Servin-Barthet and Magdalena Martínez as first authors and Òscar Vilarroya and Susana Carmona as senior authors, was published in Nature Reviews Neuroscience and will be featured on the cover of the October issue of the journal.
The researchers reviewed a total of 174 articles, in which they analyzed the connections among three fundamental areas: changes in brain structure, hormonal evolution, and maternal behavior, to open new lines of research and advance in women-oriented research.
According to the scientists, all information points to the fluctuation of hormones, mainly related to estrogens, as triggers plasticity processes in the brain during a human pregnancy and postpartum period. However, more research is needed to explain what plasticity processes (which imply changes in brain cell function, structure, and connectivity) are involved in the transition to motherhood in humans, and how they affect maternal behavior.
Motherhood and morphological changes
Motherhood is a physiologically and psychologically life-changing event, which includes a series of adaptations in how the mother behaves, aimed at ensuring the well-being of her offspring.
Researchers from the UAB and the Hospital del Mar Research Institute were the first to demonstrate in 2017 that a pregnancy implied changes in the brain morphology of first-time mothers, reducing the volume of gray matter in regions involved in social relations and that these changes were maintained for at least two years after giving birth.
Since then, researchers have observed that the brain’s gray matter changes in volume in the different stages of maternity and postpartum and is always accompanied by extreme hormone fluctuations.
In the article, researchers describe for the first time three fundamental factors in understanding the adaptation to motherhood in humans. First are estrogens (oestradiol), as the main hormone candidates in inducing changes in the brain.
Second is the brain circuit related to social cognition (involving the medial frontal cortex, precuneus, and other areas) as the specific region in which these changes occur.
Third, there are the psychological changes, i.e., the cognitive and emotional processes necessary to develop a mother-child relationship that adapts to the different pregnancy and postpartum phases. This third factor differentiates humans from other animals; yet little is known about it.
Roadmap for future research
Based on the evidence published, the researchers point out which neuroplasticity processes most likely contribute to the changes identified, and how these can be related to pregnancy and maternal behavior hormones. They also prepared a roadmap with different lines of research to advance the study of human adaptation to motherhood.
One first line of research should focus on identifying brain cell substrates. According to the experts, it is improbable that the large-scale dynamics of changes in gray matter at morphological and molecular levels be produced exclusively by plasticity. In rats, researchers observed that hormonal fluctuation, particularly at the end of the pregnancy, affects the plasticity of neurons and microglia, with a greater proliferation of this latter cell type.
A second line should work towards describing the mechanisms by which sexual hormones, especially estrogens, bring on the changes detected in structural and behavioral reorganization.
Given the hormonal environment existing during the pregnancy and postpartum period and the interactive nature of these molecules, it is most likely that these changes result from a complex exchange of steroids and hormonal peptides.
To understand this role better, research must be conducted on more hormones and metabolites, with special attention put on oxytocin and prolactin.
The third challenge focuses on identifying the psychological evolution occurring during pregnancy and postpartum and characterizing the functional changes in the brain responsible for the development of human conduct. In studies with rats, molecular and morphological changes were observed accompanied by the emergence of maternal behavior, but not so in humans.
Also, the association between neuroanatomic changes and different aspects of maternal behavior in humans are few and difficult to replicate.
Improving the methodology in MRI studies in humans and questionnaires will allow us to infer better the link between the brain changes observed and the different components of maternal behavior. All this while considering extrinsic postpartum factors, which could induce changes in the circuits related to maternal care.
A scarce number of studies conducted on women
Most studies conducted up to date have used rats. That is why the researchers put emphasis on the importance of developing research studies on women.
“There are coincidences between humans and other animals, but there are many cerebral differences, particularly on the cerebral cortex, the most evolved part of the brain, and hormonal differences, given that the choreography between sexual hormones is different in each species” explains Camila Servin, researcher from the UAB Department of Psychiatry and Legal Medicine and at the Hospital del Mar Research Institute.
“Until 2017, we had not begun to study changes in the brain occurring during pregnancy, and until now, very little has been studied on the role of hormones and the psychological environment,” explains Òscar Vilarroya, a researcher from the UAB Department of Psychiatry and Legal Medicine and at the Hospital del Mar Research Institute.
“Surprisingly, the study of what is one of the most generalized and important human experiences has never taken central stage,” the neuroscientist concludes.
About this neuroscience research news
Author: Camila Servin-Barthet
Contact: Camila Servin-Barthet – UAB
Image: The image is credited to Neuroscience News
Original Research: Closed access.
“The transition to motherhood: linking hormones, brain and behaviour” by Camila Servin-Barthet et al. Nature Reviews Neuroscience
The transition to motherhood: linking hormones, brain and behaviour
We are witnessing a stark increase in scientific interest in the neurobiological processes associated with pregnancy and maternity. Convergent evidence suggests that around the time of labour, first-time mothers experience a specific pattern of neuroanatomical changes that are associated with maternal behaviour.
Here we provide an overview of the human neurobiological adaptations of motherhood, focusing on the interplay between pregnancy-related steroid and peptide hormones, and neuroplasticity in the brain.
We discuss which brain plasticity mechanisms might underlie the structural changes detected by MRI, which hormonal systems are likely to contribute to such neuroanatomical changes and how these brain mechanisms may be linked to maternal behaviour.
This Review offers an overarching framework that can serve as a roadmap for future investigations.