What Is “Momnesia”?
Often referred to as “momnesia,” “mommy brain,” “pregnancy brain,” or “baby brain,” this is forgetfulness, mental fogginess, and cognitive changes that many women may experience during pregnancy. For example, a woman could enter the kitchen and forget what she had gone there for, or she may drop her car keys in the bathroom.
Scientists know it’s a real biological phenomenon, and now have a potential explanation: Disruption of a particular brain circuit during pregnancy, when estrogen rises steadily.
In a study of laboratory mice, they injected the animals with a constant high level of estrogen to simulate the state of estrogen during pregnancy, and found that such treatment caused temporary memory impairment in the animals, but had no effect on their mood.
They found that the high estrogen in the mice acted on a neural pathway between two brain structures: the hypothalamus, a control center and integrative hub, and the hippocampus, which plays a central role in memory formation.
They found that high estrogen increases activity in hypothalamic neurons, which in turn decreases activity in the hippocampus and impairs memory.
The most obvious signs of “Momnesia” are seen during the last half of pregnancy and can occur during the postpartum period, but generally vanish after giving birth. Short-term and long-term memory can be affected, including spatial, social, and verbal memory, such as having difficulty remembering names or words, or struggling to recall familiar information.
Impact on Daily Life and Prevalence
It is not serious or even medically disabling, but it can impact daily life and self-confidence, Dr. Zheng Sun, professor of medicine at Baylor College of Medicine specializing in endocrinology and molecular biology and one of the authors of the study published in the journal Science Bulletin.
Common examples are: forgets why the room was entered; forgets where an object is; forgets what to say or the point of a conversation; requires reminders of appointments. It is common. The figure of about 80 percent reflects self-report and subjective experience, and is not the result of objective testing, Sun said. The results indicate it is not a general decline in cognitive function.
It’s not that pregnancy makes you less intelligent, Dr. Yanlin He, director of the Brain Glycemic and Metabolism Control Laboratory at Louisiana State University’s Pennington Biomedical Research Center, said, but rather the effects seem to be more nuanced and specific to certain cognitive tasks.
Mouse Experiments and Estrogen Receptors
The mouse studies provide clues as to brain activity. Estrogen is a hormone that controls a woman’s pregnancy, menstrual cycle, and puberty, stimulating physical changes needed to accommodate the fetus, stimulate fetal development, and prepare the body for childbirth. Increases in levels during pregnancy, with peak levels in the third trimester.
The researchers discovered a protein known as “estrogen receptor alpha” that is responsible for allowing estrogen into the cell.
This area is rich in brain cells known as GABAergic neurons, which usually send calming messages to other areas of the brain. The study revealed that increased estrogen levels in the mice overactivate the inhibitory signals by these neurons, and this directly impacted the hippocampus.
The researchers conducted memory tests such as object and location recognition, and found that mice with high estrogen levels were impaired in memory tests compared to those without high levels of estrogen.
The researchers also experimentally deactivated the neuronal pathway between the hypothalamus and hippocampus and found that the mice no longer suffered from the memory deficits caused by estrogen. However, when the same pathway was activated experimentally, even in the absence of higher levels of estrogen, memory was impaired in the mice.
Eliminating estrogen receptors from these neurons in the hypothalamus reversed memory problems in mice caused by estrogen, as well as by pregnancy. We suspect that a similar circuit may play a similar role in humans, although you cannot do this type of invasive study directly in humans,” Sun said.
Connecting Mouse Findings to Human Studies
The researchers compared the mouse study with a study in which 70 pregnant women, some at varying stages of pregnancy and some who were not pregnant, were tested on their memory function with tests of long-term, short-term and working memory. These tests identified memory deficits that emerged in late pregnancy and were associated with elevated levels of circulating estrogen.
“Importantly, higher estrogen levels in the bloodstream were linked to worse scores on several measures of memory, even after researchers controlled for other factors that could influence memory. This gives “human proof” that supports the mechanism we found in mice, He said.
We should note, however, that we have not directly manipulated or measured this particular neural circuit in pregnant women. The human results corroborate the mouse results and do not confirm the same cause-and-effect as the mouse results, He said.
Momnesia, commonly known as pregnancy brain or baby brain, may have a specific biological explanation. New research has identified a brain circuit that appears to be affected by the sustained increase in estrogen that occurs during pregnancy. The findings provide new insight into why some pregnant women experience temporary forgetfulness and memory difficulties.
Momnesia and Pregnancy Hormones
During pregnancy, estrogen levels rise substantially, particularly toward the later stages of pregnancy. Researchers investigated whether these hormonal changes could influence brain pathways involved in memory.
The study found that elevated estrogen increased the activity of specific GABAergic neurons in the hypothalamus in mice. This increased activity reduced signaling in the hippocampus, a brain region that plays a central role in memory formation and retrieval.
Momnesia and Earlier Brain Research
Earlier research has also shown that pregnancy is associated with substantial changes in the brain. A 2024 Nature Neuroscience study mapped brain changes across pregnancy and reported widespread changes in gray matter volume and cortical thickness, along with changes in white-matter properties.
Research reviews have found that evidence regarding pregnancy-related cognitive changes is mixed. Some studies report modest effects on areas such as verbal memory and attention, while other studies have found little or no measurable difference.
Momnesia Research Opens New Questions
The new findings provide a potential biological pathway for understanding pregnancy-related memory changes, while also highlighting the need for additional human research. Future studies may help determine how hormonal changes, sleep, stress and brain remodeling interact during pregnancy.
However, the human portion of the research did not directly manipulate or measure the identified neural circuit. Researchers therefore described the human findings as supporting the proposed mechanism rather than proving that the same circuit causes memory changes in pregnant women.
Momnesia Does Not Mean Reduced Intelligence
The findings do not suggest that pregnancy causes a broad decline in intelligence. Instead, researchers described the effects as being more specific to certain memory functions.
Commonly reported experiences can include forgetting why someone entered a room, misplacing objects, losing track of conversations or having difficulty recalling familiar information. These experiences can be temporary and may become less noticeable after pregnancy.
Momnesia and the Hypothalamus-Hippocampus Pathway
The researchers focused on communication between the hypothalamus and hippocampus. Experiments suggested that increased activity along this pathway could impair memory performance.
When researchers experimentally disabled the pathway in mice, the observed memory problems disappeared. Conversely, activating the pathway produced memory impairment even without elevated estrogen, providing evidence that the circuit plays an important role in the process.
Momnesia Study Includes Human Participants
Researchers also evaluated memory in 70 women at different stages of pregnancy and compared their performance with non-pregnant participants. Higher circulating estrogen levels were associated with poorer performance on several memory-related measures.
Momnesia may be connected to the major hormonal changes that occur during pregnancy. Researchers found that elevated estrogen levels may influence brain activity and affect memory-related processes. This provides a potential biological explanation for why Momnesia can occur during pregnancy.
Momnesia and Brain Communication
Researchers identified communication between the hypothalamus and hippocampus as an important pathway in the study. Changes in this pathway may contribute to Momnesia by influencing how memories are processed and recalled. The findings offer new clues about the neurological basis of Momnesia.
Momnesia and the Hippocampus
The hippocampus plays an important role in learning and memory. Research suggests that hormonal signals associated with pregnancy can influence circuits connected to the hippocampus. These findings may help explain why Momnesia is commonly associated with forgetfulness and changes in memory during pregnancy.
