Researchers have identified a potential neurological mechanism behind the common cognitive changes often referred to as “pregnancy brain,” “mummy brain,” or “mumnesia,” characterized by forgetfulness and mental fogginess during pregnancy. The study, conducted using laboratory mice and complemented by assessments of pregnant women, suggests that elevated levels of the hormone oestrogen during pregnancy disrupt a specific brain circuit involved in memory formation.

The experiments, led by teams from Baylor College of Medicine and Louisiana State University’s Pennington Biomedical Research Center, involved mimicking the sustained high oestrogen levels typical of late pregnancy in mice. The researchers found that elevated oestrogen increased activity in neurons within the hypothalamus, a central brain region that regulates many physiological processes. This heightened hypothalamic activity then suppressed function in the hippocampus, a region critical for memory formation, resulting in temporary memory impairments in the animals.

“Our findings indicate that increased oestrogen boosts inhibitory signals from a specific population of hypothalamic neurons, which in turn reduces hippocampal activity and impairs memory,” said Zheng Sun, a professor of medicine and endocrinology at Baylor College of Medicine. The mice exhibited difficulties with memory tasks such as recognizing objects and locations, effects that were reversible when the neuronal pathway between the hypothalamus and hippocampus was experimentally disabled.

Further experiments showed that removing oestrogen receptors from these hypothalamic neurons prevented the memory deficits typically induced by high oestrogen, supporting a direct role for this hormone and circuit in pregnancy-related memory changes. The researchers noted that while these invasive manipulations cannot be performed in humans for ethical reasons, similar mechanisms might underlie the cognitive symptoms pregnant women report.

To investigate this possibility, the team tested memory performance in 70 women, including pregnant individuals at different stages and non-pregnant controls. The results showed that memory impairments, particularly in long-term, short-term, and working memory tasks, were most evident during late pregnancy and correlated with heightened circulating oestrogen levels. Yanling He, director of the Brain Glycemic and Metabolism Control Laboratory, said the human findings align with the mouse data but emphasized that causality cannot be definitively established in the human study.

Pregnancy brain is widely recognized among pregnant women, with about 80 percent reporting subjective changes such as forgetfulness, misplacing items, or losing the thread of conversations, though objective testing has been less consistent. Experts underline that these effects are not indicative of a general decline in intelligence but rather involve subtle disruptions in specific cognitive functions. The symptoms typically emerge in late pregnancy and may continue into the postpartum period before largely resolving after childbirth.

While the phenomenon affects daily functioning and confidence, researchers stress that it is not medically disabling. The study advances understanding of the neurobiological basis for pregnancy-associated cognitive changes and may help alleviate concerns for pregnant individuals experiencing these common symptoms.