Your brain changes shape in step with your cycle
Over a typical cycle, estradiol in the blood rises about eightfold and progesterone about eightyfold. Neuroscientists at the University of California, Santa Barbara noticed how little anyone knew about what the brain does in response.
So one of the authors, 23-year-old Laura Pritschet, gave blood and went straight into an MRI scanner every day for 30 days. Caitlin Taylor and colleagues (NeuroImage, 2020) measured the medial temporal lobe, the region that holds the hippocampus. As progesterone climbed, some areas grew and others shrank. Estradiol showed no link, and the volume of the hippocampus as a whole tracked neither hormone.
She then repeated the same 30 days on a hormone regimen that suppressed progesterone by about 97%. The link held, weakened, in only one of the four areas. That is one woman. In 2024, Rizor and colleagues (Human Brain Mapping) scanned 30 women at three points in the cycle: during their period, at ovulation and in the middle of the second half. The fine structure of white matter and the thickness of the cortex rose and fell with hormone levels in regions across the brain, while total brain volume stayed the same.
Both studies measured structure. Neither tested memory or mood, so what these shifts mean for how you think or feel is still unknown. Your body changes across the cycle, and the brain is part of the body.
Sources
- 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; 220: 117125. doi:10.1016/j.neuroimage.2020.117125
- Rizor EJ, Babenko V, Dundon NM, Beverly-Aylwin R, Stump A, Hayes M, Herschenfeld-Catalan L, Jacobs EG, Grafton ST. Menstrual cycle-driven hormone concentrations co-fluctuate with white and gray matter architecture changes across the whole brain. Human Brain Mapping, 2024; 45(11): e26785. doi:10.1002/hbm.26785