Related: Long COVID Could Mess With Menstruation in a Horrid Feedback Loop<\/a><\/strong><\/p>\n “These results are the first to report simultaneous brain-wide changes in human white matter microstructure and cortical thickness coinciding with menstrual cycle-driven hormone rhythms,” the researchers wrote<\/a>.<\/p>\n “Strong brain-hormone interaction effects may not be limited to classically known hypothalamic-pituitary-gonadal-axis (HPG-axis) receptor-dense regions.”<\/p>\n Menstruation typically means experiencing some 450 or so periods during the course of a lifetime, so understanding their effects on the body is important.<\/p>\n Yet, despite affecting roughly half the world’s population for half their lives<\/a>, research has been somewhat lacking<\/a>. Who knows why. Total mystery<\/a>. Seriously<\/a>.<\/p>\n Most of the research on the hormonal effect on the brain has been focused on neural communication during cognitive tasks, not on structural changes themselves.<\/p>\n “Cyclic fluctuations in HPG-axis hormones exert powerful behavioral, structural, and functional effects through actions on the mammalian central nervous system,” Rizor, Babenko, and their team noted<\/a>. “Yet, very little is known about how these fluctuations alter the structural nodes and information highways of the human brain.”<\/p>\n The microstructure of white matter<\/a> \u2013 the fatty network of neuronal fibers that transfer information between regions of gray matter \u2013 has been found to change with hormonal shifts, including puberty, oral contraception use, gender-affirming hormone therapy, and post-menopausal estrogen therapy.<\/p>\n To address the menstruation gap in our understanding, the team took MRI<\/a> scans of their subjects during three menstrual phases: menses, ovulation, and mid-luteal<\/a>. At the time of each of these scans, the researchers also measured the participants’ hormone levels.<\/p>\n The results showed that, as hormones fluctuate, gray and white matter volumes change too, as does the volume of cerebrospinal fluid.<\/p>\n In particular, just before ovulation, when the hormones 17\u03b2-estradiol<\/a> and luteinizing hormone<\/a> rise, the brains of the participants showed white matter changes suggesting faster information transfer.<\/p>\n Follicle-stimulating hormone<\/a>, which rises before ovulation, and helps stimulate the ovary follicles, was associated with thicker gray matter.<\/p>\n Progesterone<\/a>, which rises after ovulation, was associated with increased tissue and decreased cerebrospinal fluid volume.<\/p>\n What this means for the person driving the brain is unknown, but the research lays the groundwork for future studies, and perhaps understanding the causes of unusual but severe period-related mental health problems<\/a>.<\/p>\n A separate study published in 2024<\/a> by an international team of scientists found each phase of the menstrual cycle had a distinct influence over the brain as a whole, with changes across the brain and in specific regions found to also be related to an individual’s age.<\/p>\n “Although we do not currently report functional consequences or correlates of structural brain changes, our findings may have implications for hormone-driven alterations in behavior and cognition,” the researchers wrote.<\/a><\/p>\n “Investigation of brain-hormone relationships across networks is necessary to understand human nervous system functioning on a daily basis, during hormone transition periods, and across the human lifespan.”<\/p>\n![\"menstrual](\"https:\/\/www.europesays.com\/us\/wp-content\/uploads\/2025\/10\/menstruation_cycle.jpg\")
(Rujirat Boonyong\/Getty Images)<\/p>\n![\"white](\"https:\/\/www.europesays.com\/us\/wp-content\/uploads\/2025\/10\/white_matter_tracts.jpg\")
White matter tracts connecting regions in the human brain. (Thom Leach\/Science Photo Library)<\/p>\n