“Depending on the length of your cycle, your brain is on a roller coaster ride about every 28 days,” he said. Erica Comasko, associate professor of women’s and child health at Uppsala University in Sweden, was not involved in the study. “The importance of these studies is that we are building knowledge about the effects of hormonal fluctuations on brain structure.”
“These brain changes may or may not change how we actually act, think, and feel in our daily lives. Therefore, an important next step for science is to add pieces of the puzzle. It’s about assembling it.” Adrian Beltz, an associate professor of psychology at the University of Michigan, was also not involved in the study. “Do hormonal effects on brain structure affect brain function?”
How hormones drive the menstrual cycle
During menstruation, the beginning of a woman’s menstrual cycle, hormone levels are low. However, they increase dramatically in a few weeks.
Estrogen levels in the blood increase 8-fold about 14 days after ovulation, and progesterone levels increase 80-fold about 7 days later. The production of follicle-stimulating hormone stimulates the growth of the follicle into a mature egg, and a surge of luteinizing hormone causes the release of the egg.
A single cycle repeats every 24 to 38 days until you enter menopause. So, during menopause, the average woman experiences: 450 cycles Throughout her life.
Brain changes during the menstrual cycle
Viktoriya Babenko, a doctoral candidate at the University of California, Santa Barbara, and her former colleagues used advanced techniques in magnetic resonance imaging (MRI) to study the entire brain during three menstrual cycles. We mapped the structural changes in Stages: ovulation, menstruation, mid-luteal phase.
The midluteal phase occurs between ovulation and menstruation and is characterized by a peak in progesterone. The participants (30 young women with normal menstrual cycles) also had blood drawn to accurately record their hormone levels at the time of the scan. resultThe paper, which has not yet been peer-reviewed, was posted to the preprint database bioRxiv on October 10.
As the researchers observed when imaging the brain’s white matter, higher concentrations of estrogen and luteinizing hormone showed changes that suggested faster information transmission. White matter is deep brain tissue made up of nerve fibers that relay information to and from the outermost part of the cerebral cortex, known as the gray matter. The gray matter became thicker due to increased follicle-stimulating hormone.
Follicle-stimulating hormone was “generally positively correlated with cortical thickness throughout the brain,” he said. Elizabeth Riser, a doctoral candidate in dynamic neuroscience at the University of California, Santa Barbara, is one of the study’s authors. “Progesterone, on the other hand, was the opposite; it was generally associated with thinner cortical thickness in most regions.”
the other one is studyIn a paper published Oct. 5 in Nature Mental Health, 27 healthy participants were examined at high resolution during six menstrual cycle stages: menstrual, preovulatory, ovulatory, postovulatory, midluteal, and premenstrual. Scanned with MRI. The researchers focused on areas around the hippocampus and medial temporal lobe, which support a wide range of cognitive and emotional functions. They conducted blood draws at each of six time points to correlate brain changes with estrogen and progesterone levels.
Increased estrogen was associated with enlargement of the parahippocampal cortex, a gray matter cortical region that plays a role in memory encoding and retrieval. Elevated progesterone was associated with increased volume in the perirhinal cortex, an area that receives sensory information and is also important for memory. And the combination of high estrogen and low progesterone was associated with an enlargement of areas of the hippocampus that are essential for health. autobiographical memory.
The two studies looked at different anatomical features of the brain, so the results cannot be directly compared. The first scanned the entire brain, including white matter, to measure cortical thickness, and the second zoomed in on her one gray matter region of the brain to analyze cortical volume. However, both confirm that brain morphology consistently changes throughout the menstrual cycle, coinciding with hormone levels.
“For most women, for most of their lives, the ebb and flow of hormones in the menstrual cycle is as steady as the ebb and flow of the tides,” said the authors of the preprint study. Emily Jacobs, associate professor of psychology and brain sciences at the University of California, Santa Barbara. “We know that hormones drive physiological functions throughout the body, so we can think of this pulse like a vital sign. But how does it affect the human brain? , no one really knew.”
The dramatic effects of estrogen on the brain
In the early 1990s, a groundbreaking experiment revealed a dramatic effect of estrogen on the brain of female rats.scientists counted the number dendritic spines — Small projections along the branches of neurons that act as contact points from one cell to the next in the hippocampus over the four- to five-day menstrual cycle of rodents. Increasing the density of dendritic spines strengthens connections between neurons in the brain.
At the beginning of the cycle, when estrogen is low, dendritic spine density is at its lowest point. Over the next few days, estrogen levels gradually rise and reach their peak. During this period, more vertebrae begin to proliferate, increasing spine density by about 30%. Near the end of the cycle, the vertebrae retract and the process begins again.
The present results suggest that similar periodic fluctuations in neurons may occur in humans as well.
“This study builds a very solid foundation for future research investigating whether brain structure influences brain function and behavior, and whether this is relevant to mental health. “It will be,” Comasko said.
Have questions about human behavior or neuroscience? Email BrainMatters@washpost.com I may answer that in a future column.