Menstrual Cycle Hormones May Reshape the Brain, Study Finds

Hormones and the brain during the menstrual cycle

The continual rise and fall of hormones that regulate the menstrual cycle affects more than reproductive organs: it also changes the brain. A 2023 study offers a clearer picture of this process.

A research group led by University of California, Santa Barbara neuroscientists Elizabeth Rizor and Viktoriya Babenko followed 30 women throughout their menstrual cycles. As participants’ hormone profiles changed, the scientists recorded corresponding alterations in brain structure.

The peer-reviewed research indicates that structural changes in the brain during menstruation may extend beyond areas traditionally linked with the menstrual cycle.

"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.

"Strong brain-hormone interaction effects may not be limited to classically known hypothalamic-pituitary-gonadal-axis (HPG-axis) receptor-dense regions."

Why menstrual cycle research matters

Over a lifetime, menstruation generally involves around 450 periods, making its effects on the body important to understand.

Even though menstruation affects approximately half of the global population for half of their lives, it has received relatively limited research attention. Who knows why. Total mystery. Seriously.

Much of the existing research into hormones’ effects on the brain has examined neural communication during cognitive tasks rather than structural changes in the brain itself.

"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. "Yet, very little is known about how these fluctuations alter the structural nodes and information highways of the human brain."

White matter microstructure – the fatty web of neuronal fibres that carries information between grey-matter regions – has previously been shown to shift alongside hormonal changes. These include puberty, use of oral contraception, gender-affirming hormone therapy, and oestrogen therapy after menopause.

MRI scans reveal structural brain changes

To help fill this gap in knowledge about menstruation, the researchers carried out MRI scans at three stages of participants’ cycles: menstruation, ovulation, and the mid-luteal phase. The team also measured each participant’s hormone levels when every scan was taken.

Their results found that fluctuations in hormones were accompanied by changes in grey- and white-matter volume, as well as in the volume of cerebrospinal fluid.

Immediately before ovulation, when 17β-estradiol and luteinising hormone increase, participants’ brains displayed white-matter changes consistent with quicker information transfer.

Follicle-stimulating hormone, which rises before ovulation and helps stimulate ovarian follicles, was linked with thicker grey matter.

Progesterone levels rise after ovulation and were associated with more tissue and a lower volume of cerebrospinal fluid.

What these changes mean for the person whose brain is undergoing them remains unclear. However, the work provides a basis for future research and may ultimately help explain the causes of unusual yet severe mental-health problems related to periods.

A separate 2024 study from an international team of scientists found that every menstrual-cycle phase exerted a distinct effect on the brain overall. It identified changes throughout the brain and in particular regions, which were also connected to an individual’s age.

"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.

"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."

The findings are reported in Human Brain Mapping.

An earlier version of this article was published in October 2023.