Pregnancy Brain: Study Identifies a Possible Biological Cause of Memory Changes
Forgetting why you walked into a room, misplacing your keys, or suddenly losing track of a conversation are experiences many women report during pregnancy. Often described as “pregnancy brain” or “momnesia,” these temporary changes in memory have long been recognized, but their biological basis has remained unclear.
A new study published in Science Bulletin has identified a specific brain circuit that may help explain pregnancy-related memory changes. The research suggests that sustained high levels of estrogen during pregnancy can affect communication between the lateral hypothalamus and the hippocampus, temporarily disrupting certain memory functions.
What Happens in the Brain During Pregnancy?
The study, titled “High-level estrogen impairs memory via estrogen receptor signaling in a hypothalamic–hippocampal neural circuit,” examined how prolonged exposure to high estrogen levels affects memory. The research was conducted by scientists from Baylor College of Medicine and collaborating institutions, including Shandong University and Pennington Biomedical Research Center.
Researchers first used mice to reproduce the sustained high estrogen levels associated with pregnancy. They found that elevated estrogen increased the activity of GABAergic neurons in the lateral hypothalamus. These neurons project to the hippocampus, a brain region essential to learning and memory.
The increased activity of this pathway suppressed hippocampal activity and was associated with temporary impairments in memory, including performance on tests involving recognition of objects and their locations.
The researchers also found evidence that estrogen receptor signaling was central to the process. When the hypothalamus-to-hippocampus pathway was experimentally suppressed, the memory problems observed in the mice disappeared. Conversely, activating the pathway produced memory impairment even without elevated estrogen levels.
Removing estrogen receptors from the relevant hypothalamic neurons also prevented estrogen- and pregnancy-related memory problems in the mice, providing evidence of a causal mechanism within the animal model.
What Did the Human Study Show?
To examine whether the findings were also reflected in women, the researchers assessed memory performance in 70 women, including participants at different stages of pregnancy and non-pregnant participants.
The women completed tests covering long-term, short-term, and working memory. The researchers observed task-specific memory difficulties during late pregnancy, which were associated with higher levels of circulating estrogen, even after accounting for other potential factors.
However, the human findings have an important limitation. The researchers did not directly measure or manipulate the hypothalamus-to-hippocampus circuit in pregnant women. As a result, the human data support the proposed mechanism identified in the animal experiments but do not establish the same cause-and-effect relationship in humans.
Does Pregnancy Brain Mean a Decline in Intelligence?
The findings do not indicate that pregnancy causes a general decline in intelligence or cognitive ability. Instead, the research points to more specific and temporary changes affecting certain memory-related tasks.
Dr. Zheng Sun, an Associate Professor in the Department of Medicine, Division of Endocrinology, Diabetes and Metabolism, and the Department of Molecular and Cellular Biology at Baylor College of Medicine, is one of the study’s leaders. Baylor College of Medicine identifies Sun as a researcher whose work focuses on the regulation of energy metabolism and neurocognition.
The researchers noted that pregnancy-related memory changes can affect everyday activities and may be most noticeable during later pregnancy. They may also continue into the postpartum period before generally becoming less noticeable after childbirth.
Overall, the study provides new evidence for a biological explanation of “pregnancy brain,” while highlighting the need for further research to determine whether the same neural circuit identified in mice operates in the same way in pregnant women.
