New research shows that women’s brains change during the menstrual cycle

New research shows that women’s brains change during the menstrual cycle

A woman’s menstrual cycle depends on the ebb and flow of hormones that prepare the body for pregnancy. This symphony of hormones not only transforms the reproductive organs, but, according to recent research, it also reshapes the brain.

Two studies released in October detailed women’s brain scans at multiple points during the menstrual cycle and found that the size or thickness of certain areas changes in conjunction with hormone levels. The brain areas highlighted by both studies are those in the limbic system, a group of brain structures that govern emotions, memory, and behavior.

“It’s like the brain is on a roller coaster every 28 days or so, depending on the length of the cycle,” said Erika Comasko, an assistant professor of women’s and children’s health at Uppsala University in Sweden, who was not involved in the research. “The importance of these studies is that they build knowledge about how these hormonal fluctuations affect how the brain is structured.”

“These changes in the brain may or may not change the way we act, think and feel in our daily lives. Important next steps for science are to put together the pieces of the puzzle,” said Adrienne Peltz, an assistant professor of psychology at the University of Michigan, who was also not involved in the research. Together.” “Do hormonal influences on brain structure affect how the brain works?”

How hormones drive the menstrual cycle

During a woman’s menstrual cycle, which marks the beginning of menstruation, hormones are at low levels. But it rises significantly within a few weeks.

Blood estrogen levels become eight times higher at ovulation around day 14, while progesterone levels increase 80-fold about seven days later. The production of follicle-stimulating hormone stimulates the growth of an ovarian follicle into a mature egg, while a rise in luteinizing hormone triggers the release of an egg.

One cycle repeats every 24 to 38 days until the transition to menopause, which means the average woman experiences about 450 menstrual cycles throughout her life.

Changes in the brain during the menstrual cycle

Victoria Babenko, who conducted the research as a doctoral candidate at UC Santa Barbara, and her former colleagues at the university used advanced magnetic resonance imaging (MRI) methods to map structural changes in the entire brain over three menstrual cycles. Stages: ovulation, menstruation, and mid-luteal.

The midluteal phase occurs between ovulation and menstruation, and is characterized by a peak in progesterone. The participants – 30 young women with normal cycles – also had their blood drawn to accurately record their hormone levels at the time of the scan. The results, which have not yet been peer-reviewed, were published on October 10 on the preprint database bioRxiv.

Higher concentrations of estrogen and luteinizing hormone were associated with changes that indicate faster transmission of information, as the researchers saw when imaging the brain’s white matter. White matter is deeper brain tissue made up of nerve fibers that transmit information to and from parts of the outer cerebral cortex, known as gray matter – which in turn becomes thicker as follicle-stimulating hormone rises.

FSH “was positively associated with cortical thickness, generally across the entire brain,” said Elizabeth Rezor, a doctoral candidate in dynamic neuroscience at the University of California, Santa Barbara, and one of the study’s authors. “While progesterone was somewhat the opposite, it was generally associated with less cortical thickness in most areas.”

The other study, published in the journal Nature Mental Health on October 5, scanned 27 healthy participants using high-resolution MRI during six phases of the menstrual cycle: menstrual, pre-ovulatory, ovulatory, post-ovulatory, and mid-luteal, And before menstruation. The researchers focused on the hippocampus and areas surrounding the medial temporal lobe, which support a wide range of cognitive and emotional functions. They drew blood at each of the six time points to correlate brain changes with estrogen and progesterone concentrations.

Increases in estrogen have been linked to expansion of the parahippocampal cortex, a cortical region of gray matter that plays a role in memory encoding and retrieval. Higher progesterone was associated with greater volume in the perirhinal cortex, an area that receives sensory information and is also important for memory. High estrogen and low progesterone were associated with enlargement of the hippocampus, an area essential for autobiographical memory.

The two studies looked at different anatomical features of the brain, so their results cannot be directly compared. The first scanned the entire brain, including white matter, and measured cortical thickness, while the second zoomed in on a single region of gray matter in the brain and analyzed cortical volume. However, both emphasize that the shape of the brain changes across the menstrual cycle, consistently and synchronously with hormone levels.

“For most women, for most of our lives, this ebb and flow of hormones across the menstrual cycle is as constant as the ebb and flow,” said pre-print study author Emily Jacobs, assistant professor of psychological and brain sciences at UC Santa Fe. Barbara. “You can think of this pulse as a vital sign because we know that hormones drive physiological functions throughout the entire body. But no one really knows how that affects the brain in humans.

The dramatic effects of estrogen on the brain

In the early 1990s, a pioneering experiment revealed the dramatic effects of estrogen on the brains of female rats. The scientists counted the number of dendritic spines — small protrusions along the branches of neurons that act as cell-to-cell communication points — in the hippocampus across the rodents’ 4- to 5-day menstrual cycle. The greater density of dendritic spines translates into enhanced communication between neurons in the brain.

At the beginning of the cycle, when estrogen is low, dendritic spine density is lowest. Over the next few days, estrogen levels gradually rise and reach their peak. During this time, more spines begin to multiply, and spine density increases by about 30 percent. At the end of the cycle, the spines retract, and the process begins again.

The current results suggest that similar periodic fluctuations in neurons can occur in humans as well.

“The studies build a very strong foundation for future studies to see if brain structure has an impact on brain function and behavior, which will then become relevant to mental health,” Comasco said.

Do you have a question about human behavior or neuroscience? e-mail We may answer it in an upcoming column.

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