Due to the menstrual cycle, a woman’s hormone levels fluctuate over the course of a month – and even influence the appearance of her brain. A study shows that the volume of the hippocampus in the female brain increases when estrogen levels are high around ovulation. The hippocampus and surrounding temporal lobe are associated with memory and control of emotions. However, it is still unclear to what extent the cycle-related volume change affects mood and mental performance.
Over the course of a month, hormone levels fluctuate in women of reproductive age. At the beginning of the cycle, estrogen levels rise and reach a maximum around ovulation. In the second half of the cycle, progesterone dominates. The interplay of hormones ensures that the uterine lining is prepared for the possible implantation of a fertilized egg. However, female sex hormones also have effects in other parts of the body: studies on rodents and non-human primates have shown that the brain structure changes cyclically with hormone levels. A study on a single woman has provided initial evidence that this could also be the case in humans.
Volume fluctuations in the brain
Now a team led by Rachel Zsido from the Max Planck Institute for Cognitive and Brain Sciences in Leipzig has shown in 27 women that fluctuations in hormone levels are actually accompanied by changes in the brain. For the study, the researchers took blood from the test subjects six times over the course of a month to determine their hormone levels. In addition, they recorded the cycle phase using ultrasound by observing the growth of the follicles in the ovaries and ovulation. Using magnetic resonance imaging (MRI), they measured the volume of the hippocampus and other parts of the temporal lobe – a region in which many receptors for sex hormones are located.
“We found that certain regions of the medial temporal lobe, which are important for episodic memory and spatial perception, increase in volume under high estradiol and low progesterone levels – that is, these brain areas remodel in synchrony with the menstrual cycle,” reports Zsido’s colleague Julia Sacher. Under the influence of progesterone, however, the volume of the perirhinal cortex, which is also located in the temporal lobe and is associated with memory, increased.
Effects on behavior and cognition are still unclear
Studies in rodents have already suggested that hormone-related changes in brain structure also affect the ability to process new information. “Further studies are needed to clarify whether these rhythmic changes in gray matter volume are also associated with rhythmic changes in behavior in humans,” writes Emily Jacobs of the University of California, Santa Barbara, in an accompanying commentary to the study was also published in the journal “Nature Mental Health”.
Sacher and her team also want to research whether the rhythmic volume fluctuations of certain brain regions are changed in people with an increased risk of diseases such as dementia or mood disorders. “In general, the female brain is still far too little studied in neuroscience,” says Sacher. “Although we know that sex steroid hormones strongly influence our learning and memory, less than 0.5 percent of the literature in this area addresses the menstrual cycle, the influence of hormonal contraceptives, pregnancy and menopause. We want to change that because in order to be able to specifically treat women with Alzheimer’s or depression, we need to better understand how the healthy female brain adapts to changes and is influenced by sex hormones.”
Source: Rachel Zsido (Max Planck Institute for Cognitive and Brain Sciences, Leipzig) et al., Nature Mental Health, doi: 10.1038/s44220-023-00125-w