There are oestrogen and progesterone receptors in the brain as well, so it lives in a changing hormonal environment every month. In 2020, researchers at the University of California, Santa Barbara studied one woman for 30 consecutive days, with a brain scan and a blood test every day. Oestrogen and progesterone levels were widely linked to how brain networks communicate with each other, especially the default mode and attention networks. The analysis suggested that the hormonal changes come first and the brain networks follow.
The hippocampus before ovulation
In a 2015 NeuroImage study, 21 women were scanned four times across the cycle. In the late follicular phase, when estradiol rises, the volume of the hippocampus, which is key for memory, was larger than in the early follicular phase. Yet cognitive test results did not differ reliably between phases: brain structure changed, but abilities stayed stable.
Both studies are small, so they point to a direction rather than a final truth for all women. Hormonal contraception changes the natural rhythm, so these results do not apply to it directly.
What this means for you
- If you feel different on different days of your cycle, there is a biological basis for it.
- For a few months, track how you feel, your sleep and your energy alongside your cycle days.
- If you notice marked changes that disrupt your life, talk to your doctor.
Sources
- Pritschet L., Santander T., Taylor C. M., Layher E., Yu S., Miller M. B., Grafton S. T., Jacobs E. G. (2020). Functional reorganization of brain networks across the human menstrual cycle. NeuroImage, 220, 117091. Link
- Lisofsky N., Mårtensson J., Eckert A., Lindenberger U., Gallinat J., Kühn S. (2015). Hippocampal volume and functional connectivity changes during the female menstrual cycle. NeuroImage, 118, 154–162. doi:10.1016/j.neuroimage.2015.06.012