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If a woman suddenly becomes moody, others may ask if "those days of the month have arrived." If she feels horny, others will say that she may be ovulating. As it turns out, this is not unfounded – some women do feel more anxious and irritable during their periods, and have a higher libido at the time of ovulation (not that these manifestations are set in stone, of course, but can often be explained this way). （www.tandfonline.com/doi/abs/10.1080/03630242.2015.1101739）（www.sciencedirect.com/science/article/pii/S0018506X13000482）
But what few people know is that the menstrual cycle can also have a positive effect on a woman's brain. It has been proven that after menstruation, women improve certain skills, such as spatial awareness. After three weeks, women's verbal skills are at their peak. And, oddly enough, they are much better at discerning when someone is frightened. Also, at some point during menstruation, a woman's brain actually gets bigger. What's going on?(pubmed.ncbi.nlm.nih.gov/11749982/)(www.ncbi.nlm.nih.gov/pmc/articles/PMC4834434/)
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Elma Jashim is a recent college graduate looking forward to starting medical school in the fall. But she is also concerned about mood swings in her monthly menstrual cycle and how seriously it can interfere with her busy school schedule. "About two or three days before my period started, I felt less emotional, less upset and less excited," Jashim said. When Jassim's period begins, this period of emotional stabilization increases her sensitivity to even small emotional stimuli. "If I make a small mistake at work, I'm almost always going to crash. "It's unclear what exactly happened in her brain that triggered these emotions. But progress is being made in visualizing how sex hormones alter certain areas of the brain. Previous studies in rats and other mammals have shown [1][2] that the volume of specific brain regions can be altered under the action of estrogen, which is required for female sexual and reproductive development. But it remains to be seen whether this potent hormone will alter the structure of the human female brain.
© George Wylesol
Recent MRI scans of women's brains show that sex hormones rise and fall during the menstrual cycle — a 29-day cycle in which sex hormones rise and fall in preparation for a possible pregnancy, dramatically altering the areas of the brain that control mood, memory, behavior and the efficiency of messaging. "It's amazing to see how quickly the adult brain can change," says Julia Sacher, a psychiatrist and neuroscientist at the Max Planck Institute for Human Cognition and Brain Sciences in Leipzig, Germany, who led one of the studies [3]. Catherine Woolley, a neurobiologist at Northwestern University in Evanston, Illinois, notes that changes in the brain throughout the menstrual cycle are particularly noteworthy, as most women experience nearly 450 menstrual cycles over a period of 30 to 40 years [4]. The advantage of these studies, Woolley says, is that brain imaging and hormone measurements are done at the same stage of a person's menstrual cycle. Emily Jacobs, a neuroscientist at the University of California, Santa Barbara, said, "Through these studies, we now understand how much these hormones play a role in shaping the morphology and functional structure of the brain." ”
Hormone-driven menstrual cycles The menstrual cycle repeats every 25 to 30 days and begins with a "menstrual period" or shedding of the endometrium. At the beginning of the cycle, estrogen levels in the blood are at their lowest, but rise dramatically over the next few weeks. First, estrogen levels rise, marking endometrial growth. Estrogen levels then drop and the ovaries release eggs, marking the midpoint of the menstrual cycle. After that, progesterone and estrogen levels increase again for about 7 days, preparing the endometrium for possible egg fertilization. If you are not pregnant, both estrogen and progesterone levels drop, triggering menstrual bleeding. Although the menstrual cycle is caused by significant fluctuations in hormone levels, other hormones, such as testosterone and cortisol, can also fluctuate in cycles: rising before dawn and falling in the evening [5]. These daily rhythms are present in both sexes [6].
Estrogen stimulates cognitive areas of the brainThe brain is densely packed with cells called neurons, each of which looks like a miniature tree. Gray matter is the outer layer of brain tissue that contains neurons and short branches called dendrites. The leaf-like protrusions on the dendrites are called dendritic spines. The roots of neurons, also known as axons, are packed in the white matter of the brain. Gray matter is responsible for regulating mood, learning, and memory, while white matter, located deep in the brain tissue, is responsible for exchanging information and connecting different gray matter regions.
© Wikipedia
The regions of the brain that respond to female sex hormones were first discovered about 30 years ago. In 1990, Woolley stumbled upon the fact that estrogen regulates dendritic spine density in the hippocampus of the rat brain [7]. "It was a very surprising result that raised considerable skepticism in the field," Woolley recalled, "because at the time, estrogen was thought to be only reproductive hormones and did not affect cognitive areas of the brain like the hippocampus." "The hippocampus — the cognitive center of the brain that contains both gray and white matter — is a small, curved structure buried deep in the brain behind the ear and is densely populated with sex hormone receptors. The hippocampus is also the most sensitive area of the adult brain to changes in volume. Learning a new skill, such as juggling in later years, or taking a London taxi licence test by taking a map, can make the hippocampus bigger. On the other hand, atrophy of the hippocampus may be an early sign of dementia, especially Alzheimer's disease [8]. Since Woolley's groundbreaking discovery, scientists have learned that menopause reduces gray matter volume in certain parts of the brain. However, the study was limited to snapshot observations of the volunteers' brains at a single time point. Scientists want to know whether an adult's brain changes during the monthly rise and fall of sex hormones. "Can we be very precise? Can we pick a person and measure their brain 30, 50, or 100 times?" Jacobs thought. This prompted a scientist in Jacobs' team to scan his brain every 24 hours for an entire month in 2020. "She's like Mary Curie in neuroscience," Jacobs said. From the woman's 30 brain scans, Jacobs' team found that sex hormones remodeled the hippocampus and reorganized the brain's connections. However, it is unclear how quickly hormonal fluctuations during the menstrual cycle can do this [9]. To address this, scientists in Leipzig and Santa Barbara have now each performed brain scans of more than 50 women at multiple points in their menstrual cycles for two unrelated studies.
In a study published in the journal Nature Mental Health [10], Julia Sach's team used ultrasound to determine the precise timing of ovulation in 27 female volunteers. This allowed them to take blood samples at 6 precise time points of the volunteers' menstrual cycle, which are related to ovulation and hormone levels in the blood. Subsequently, they used ultrahigh-field MRI to scan the brains of the 27 women at six specific time points. With this more powerful magnetic resonance imaging technique than is commonly used in the clinic, Sach's team can obtain high-resolution images of the living brain, which was previously only possible by directly slicing the brain during an autopsy.
© nature
Despite the very small structure of the hippocampus, Sahe's team was able to observe a series of coordinated changes that occur in different areas of the hippocampus with the menstrual cycle. As estrogen levels rise and progesterone levels fall, the outer layer of the hippocampus thickens and the gray matter expands. But when progesterone (progesterone) levels rise, the areas associated with memory expand. Another study, which has not yet been peer-reviewed, scanned the brains of 30 volunteers, during ovulation, menstruation, and in between. The study found that not only the thickness of gray matter fluctuated, but also the structural properties of white matter changed due to hormones. "We measured gray matter and observed that it changed in sync with hormone fluctuations," Elizabeth Rizor said. She co-led the study with Viktoriya Babenko, both neuroscientists at the University of California, Santa Barbara. The study suggests that changes in white matter due to hormonal fluctuations may lead to more efficient transmission of information between different parts of the brain [11]. "These changes are very broad and involve not only in gray matter, but also in brain regions responsible for coordination across regions and white matter pathways," Baben said. "However, changes in the volume or thickness of brain regions observed in these studies have not been correlated with specific brain functions. Although studies have shown that certain areas of the brain can remodel themselves in response to hormone fluctuations in the menstrual cycle, scientists warn that these studies do not mean that memory or cognition are affected. "We can't think that bigger is better for a particular brain function or process," Woolley said. "These studies also did not reveal whether volume changes were associated with the various emotional and cognitive symptoms experienced by women during menstruation. In fact, the studies only included healthy women who did not report any of these symptoms. Jacobs said there is an urgent need for more trials to study women's unique neuroscience needs.
一位32岁女性大脑的彩色磁共振成像（MRI）扫描。 © DR P. MARAZZI, SCIENCE PHOTO LIBRARY
"There's an actual structural change going on in our brains, which could be related to mood swings and so on," Jassim said. Although women account for 70 percent of Alzheimer's disease cases and 65 percent of depression cases, only about 0.5 percent of brain imaging studies are related to women [12]. This imbalance persists even in drug approvals, such as Lecanemab-irmb, recently approved by the U.S. Food and Drug Administration (FDA) for the treatment of early Alzheimia, which may not have a slowing effect on women's disease. "It's time to make the brain a major concern for women's health," Sach said. ”
Bibliography:
[1]linkinghub.elsevier.com/retrieve/pii/S0018506X98914660
[2]pubmed.ncbi.nlm.nih.gov/26109339/
[3]www.nature.com/articles/s44220-023-00125-w
[4]link.springer.com/article/10.1007/s10549-007-9574-z
[5]pubmed.ncbi.nlm.nih.gov/496034/
[6]doi.org/10.1101/2023.10.16.562607
[7]doi.org/10.1523/JNEUROSCI.10-04-01286.1990
[8]link.springer.com/article/10.1007/s13205-022-03123-4
[9]www.sciencedirect.com/science/article/pii/S105381192030611X?via%3Dihub
[10]www.nature.com/articles/s44220-023-00125-w
[11]www.biorxiv.org/content/10.1101/2023.10.09.561616v1
[12]www.nature.com/immersive/d41586-023-01475-2/index.html
文/Sanjay Mishra
Translated by tempura
Proofreading/Bunny's Limbo microstep
Original/www.nationalgeographic.com/premium/article/menstruation-brain-women-reshape
This article is licensed under a Creative Commons (BY-NC) license and is published by Tempura in Leviathan
The views expressed in this article are those of the author and do not necessarily reflect the views of Leviathan
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