If you have been getting your period for any number of years, you may have noticed changes in energy, mood, emotions, memory, and sexual desire over the course of your cycle [1].
No, you’re not crazy. You have your hormones to thank for this. In fact, recent research has shown that the dramatic hormonal changes you experience over the course of your menstrual cycle can actually cause changes to your brain. These hormonally-driven brain changes aren’t just caused by your menstrual cycle; they can occur from pregnancy, perimenopause, and menopause, too [2].
Advancements in brain imaging technology over the last few decades have vastly improved our understanding of how hormonal fluctuations impact the female brain (even if there’s still so much we don’t yet know). For example, a 2019 study looked at brain activity while a 2023 study looked at structural changes to the brain throughout the menstrual cycle [3][4]. Here, let’s look at how hormonal changes during the phases of your cycle may affect brain activity and even brain structure.
Estrogen and progesterone levels change dramatically throughout the menstrual cycle
During the typical menstrual cycle, estradiol (the most common form of estrogen) and progesterone levels rise or fall in relation to ovulation. Estrogen gradually rises after your period is over, and then peaks right before ovulation. After ovulation, estrogen drops again and then rises slowly during the luteal phase (the phase after ovulation), dropping sharply before menstruation begins.
Progesterone levels remain low during your period and the follicular phase (the phase before ovulation), but gradually rise after ovulation and peak in the mid-luteal phase. Like estrogen, progesterone levels also fall before your period, and remain low throughout menstruation (or menses).
Hormonal changes throughout the cycle lead to changes in brain activity
In a study published in 2019 in the journal Neuropsychopharmacology, researchers from Salzburg, Austria studied thirty-six naturally cycling women in their mid-twenties (i.e., young women who were not on any hormonal therapies or birth control) [3]. The researchers performed magnetic resonance imaging (MRI) on the women while they completed a spatial navigation task and a verbal fluency task at various points in their cycles. These MRIs allowed the researchers to identify changes in brain activation as the women’s estrogen and progesterone levels changed.
Specifically, these investigators took a scan of each individual woman during menstruation, during the preovulatory (follicular) phase, and during the postovulatory (mid-luteal) phase. They focused on activation in the left and right dorsolateral prefrontal cortex (or DLPFC), and the left and right hippocampus regions of the brain. These areas were chosen because previous studies showed progesterone could activate the DLPFC and improve cognitive function, while estrogen could activate the hippocampus and improve spatial performance.
Estrogen and progesterone activate different parts of the brain
From this small study, the researchers didn’t find any significant changes in performance or brain function throughout the menstrual cycle. However, they did identify changes in brain activation patterns. During the preovulatory phase, estrogen activated the left and right hippocampus during navigational or spatial tasks, but not verbal tasks.
Later in the cycle, rising levels of progesterone led to a reduction in brain activity in the left hippocampus in both navigation and verbal tasks. Progesterone, however, increased brain activity in both the right and left DLPFC while estrogen had no significant effect on this region.
Even though brain activity changed, brain function did not
Interestingly, in this study, the researchers saw changes in brain activity over the course of the cycle, but those changes didn’t lead the women to perform better or worse on navigational or verbal performance tasks. The researchers therefore posited that compensatory mechanisms are at play to ensure your daily activities aren’t affected even as your hormones are increasing and decreasing activity in certain parts of your brain.
In a way, this is an example of “no news is good news!” That is, despite observable changes in their brain activity over the course of their cycles, the women in this study still performed the same on various tasks. This is encouraging, because you can’t always control the timing of important work meetings or family decision-making to align perfectly with the “optimal time” for these things during your cycle. While hormonally-driven changes over the course of your cycle do have an effect on your energy, thinking, and emotions (and they are certainly not “all in your head”), your intelligent brain has workarounds to ensure that you continue to function. In other words, you are more than your cycle!
Despite observable changes in their brain activity over the course of their cycles, the women in this study still performed the same on various tasks. This is encouraging, because you can’t always control the timing of important work meetings or family decision-making to align perfectly with the “optimal time” for these things during your cycle.
Hormonal changes throughout the cycle lead to changes in brain structure
In a 2023 research study published in the journal Nature Mental Health, German scientists used advanced MRI technology to study structural changes to the female brain during normal hormone fluctuations [4].
The German study focused on the extended medial temporal lobe (or MTL) region of the brain, which includes the hippocampus. They used a strategy called “dense sampling” to subdivide sections of the hippocampus to detect more subtle changes that might be obscured by looking at larger areas. These sub-regions of the hippocampus were chosen for this study because they are highly susceptible to changing hormone levels ( the region’s cells have many estrogen and progesterone receptors), and because they are essential to both memory and learning.
Changes in estrogen and progesterone correlate with changes in brain volume
The German investigators studied 27 females aged 19-34 and followed them for just one menstrual cycle. Participants had an MRI scan during menses, preovulatory, ovulation, postovulatory, mid-luteal, and premenstrual phases of their cycle. As expected, these women had the highest levels of estrogen in the preovulatory and ovulation phases, and the highest progesterone in the mid-luteal phase. The study showed changes in brain volume in the MTL and subregions of the hippocampus that corresponded with changes in estrogen and progesterone levels.
Consistent with other research in this field, the German study found that estrogen increased brain volume in the regions that corresponded with memory and cognitive processes. Progesterone diminished the effect of estrogen, and increased the volume of regions of the brain called area 35 and the subiculum (also part of the MTL), which are understudied but proposed to have effects regarding aging and neurodegeneration.
Researchers still don’t know how structural and activity changes due to cyclical hormonal fluctuations affect brain function
The Austrian and German researchers measured different parameters. While the Austrian study examined the relationship between fluctuating hormone levels and changes in behavioral or task performance, the German study assessed the connection between fluctuating hormone levels and brain structural changes. .
In both the Austrian and German studies, investigators used advanced technology to measure changes in brain activity and structure throughout the menstrual cycle. But we still don’t have measurable evidence that hormonally-driven cyclical changes in brain structure or brain activity affect functioning.
Both studies were limited by small sample sizes, with each involving fewer than forty women. Further testing is also needed to assess functional or behavioral tasks (like memory recall or verbal assessment) in combination with advanced MRI scans.
Much female brain research has been on female animals, not humans
Despite their lack of strong conclusions on the functional effects of brain changes over the course of the female menstrual cycle, these studies and others like them are groundbreaking in the field of mental health research and women’s health.
To date, most of the research regarding female brain function has been done on rats instead of humans. Historically, women haven’t been included (or have been underrepresented) in research studies, whether of medicines or health conditions or diseases. And even when women have been studied, they’ve often been required to be on hormonal birth control to prevent unintended pregnancies and to remove fluctuating hormones from the equation. For these reasons, studies focused on women’s hormones are still new in the field. The fact that some investigators now acknowledge women’s changing hormones and want to study them (without trying to manipulate or suppress them) is a huge leap forward in the field of women’s health.
The fact that some investigators now acknowledge women’s changing hormones and want to study them (without trying to manipulate or suppress them) is a huge leap forward in the field of women’s health.
The bottom line on how the menstrual cycle changes the brain
Hormones, particularly estrogen and progesterone, fluctuate predictably throughout the female menstrual cycle. Studies have linked these hormonal changes to changes in brain activity, structure, and volume. However, the measurable effect of hormones on brain function or task performance is still conflicting–although that doesn’t stop some from making broad brush-conclusions like “memory is sharpest before ovulation!”
Additional studies that combine brain scanning technology with neuronal functional testing will hopefully shed some light on the roles of estrogen and progesterone outside of regulating fertility. For now, know the female brain does change over the course of the menstrual cycle, but the research is just beginning to connect specific changes to measurable differences in performance–and that no matter what phase we’re in, our intelligently designed female brains seem to have some sort of compensatory mechanisms built in to keep us functioning well.
References:
[1] Bullivant SB, Sellergren SA, Stern K, Spencer NA, Jacob S, Mennella JA, McClintock MK. Women’s sexual experience during the menstrual cycle: identification of the sexual phase by noninvasive measurement of luteinizing hormone. J Sex Res. 2004 Feb;41(1):82-93. doi: 10.1080/00224490409552216. PMID: 15216427. [2] Elisa Rehbein, Jonas Hornung, Inger Sundström Poromaa, Birgit Derntl; Shaping of the Female Human Brain by Sex Hormones: A Review. Neuroendocrinology 18 February 2021; 111 (3): 183–206. https://doi.org/10.1159/000507083 [3] Pletzer, B., Harris, TA., Scheuringer, A. et al. The cycling brain: menstrual cycle related fluctuations in hippocampal and fronto-striatal activation and connectivity during cognitive tasks. Neuropsychopharmacol. 44, 1867–1875 (2019). https://doi.org/10.1038/s41386-019-0435-3 [4] Zsido, R.G., Williams, A.N., Barth, C. et al. Ultra-high-field 7T MRI reveals changes in human medial temporal lobe volume in female adults during menstrual cycle. Nat. Mental Health 1, 761–771 (2023). https://doi.org/10.1038/s44220-023-00125-w
[5] Taylor CM, Pritschet L, Olsen RK, Layher E, Santander T, Grafton ST, Jacobs EG. Progesterone shapes medial temporal lobe volume across the human menstrual cycle. Neuroimage. 2020 Oct 15;220:117125. doi: https://doi.org/10.1016/j.neuroimage.2020.117125
