Every month during our menstrual cycle, hormone fluctuations influence our mood, emotions, and behavior. Prior to menstruation, specifically ovulation, some of us experience symptoms including a change in basal body temperature, higher sex drive, or a heightened sense of smell, taste, or vision. Now, a recent study in Scientific Reports has revealed there’s a silent symptom on our most fertile days: brain growth.
Researchers at the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany noted the correlation between estrogen levels throughout the menstrual cycle and the female brain.
“We found, that in parallel to the rising estrogen levels leading up to ovulation, the Hippocampus also increases in volume–the volume of the grey matter as well as that of the white matter,” explains Claudia Barth, first author of the study, in a statement.
The hippocampus — a small region of the brain that forms part of the limbic system — is associated with memories, mood, and emotions. Previous research has found it can be directly affected by estrogen when it comes to synapses — where connections to other cells occur. Estrogen increases synaptic connectivity in the hippocampus by 25 percent, meaning it enhanced communication between neurons.
Barth and her team of researchers observed 30 women and measured the levels of estrogen in their blood across two full menstrual cycles. The women also underwent MRI scans, which the researchers used to measure the volume of the different regions within each woman’s brain. There was a growth in gray matter (where all the synapses are located) and white matter (where the nerve fibers are located, which are extensions of nerve cells) in the brain as estrogen levels rose, causing the hippocampus to increase in volume; the changes occurred parallel to ovulation.
It’s unclear how these monthly changes in the hippocampus’ volume impacts women’s daily lives, but Barth suspects it could alter behavior.
Hormone fluctuation throughout your menstrual cycle influences brain growth. Photo courtesy of Pexels, Public domain
“In mice it has already been proven that it is not just this brain structure but also different behaviours which underlie a type of monthly cycle,” said Barth.
Other studies have shown that a rise of estrogen levels during the menstrual cycle deters women from impulsive decision-making. A 2014 study in the Journal of Neuroscience found greater increases in estrogen levels across the menstrual cycle compared to impulsive behavior during the beginning of menstruation when estrogen levels are low. The hippocampus, hypothalamus, and the amygdala tend to be affected the most by the estrogen-progesterone surges and drops. The surges of these hormones can influence a woman’s mood, self-esteem, and how she connects to others.
“Estrogen levels are closely linked with women’s emotional well-being as estrogen affects parts of the brain that control emotions,” Dr. Ben Michaelis, a clinical psychologist in New York City and author of “Your Next Big Thing,” previously told Medical Daily.
The new research could shed light on premenstrual dysphoric disorder (PMDD), which affects one in 12 women in the days leading up to her period. Symptoms include severe mood swings and anxiety. The researchers contend if women are particularly receptive in certain phases of their cycle to making changes in their behavior, this could be a good time for PMDD patients to undergo therapy. However, they first need to find out which monthly rhythm the brain of a healthy woman follows to reveal the differences in people affected by PMDD.
Once science investigates how exactly the hippocampus influences behavior, we’ll gain a better understanding for what motivates our actions, especially during our menstrual cycle.