Ovarian hormone fluctuations shape brain structure during reproductive years

A recent study in Nature Mental Health conducted by Rachel Zsido and Julia Sacher from the Max Planck Institute for Human Cognitive and Brain Sciences and the University Clinic in Leipzig, Germany, has unveiled the connection between cyclic changes in ovarian hormone levels in women throughout their menstrual cycle and alterations in brain structure.

The impact of ovarian hormones on the brain is substantial, and there is a concern that early menopause might be linked to a higher risk of accelerated brain aging and future dementia. Nevertheless, the influence of ovarian hormone fluctuations on brain structure earlier in life has remained less clear. In their latest research, Zsido and Sacher have demonstrated that these hormonal fluctuations affect the structural adaptability of critical brain regions during a woman’s reproductive years.

In order to achieve this, the researchers gathered blood samples from 27 female participants and monitored follicle growth in the ovaries to precisely determine ovulation timing using ultrasound. They then utilized state-of-the-art 7 Tesla MRI technology to examine specific subregions of the medial temporal lobe and the hippocampus, as these areas are rich in sex hormone receptors and play a pivotal role in cognitive functions such as episodic memory.

Capturing dynamic changes in sex hormones

In contrast to earlier studies, Zsido and Sacher’s research took a more comprehensive approach by examining female brains at six different points throughout the menstrual cycle. This longitudinal design allowed them to capture the dynamic fluctuations in sex hormones. Across the menstrual cycle, estradiol, a crucial female sex hormone, increases during the first half of the cycle, peaking around ovulation, while the second half is dominated by progesterone.

Estradiol plays a vital role in maintaining the female reproductive system, while progesterone prepares the uterus for potential pregnancy and offers anxiety-relief, sleep-induction, and relaxation effects. This study unravels how the female brain harmonizes with the rhythmic dance of hormones, akin to the ebb and flow of tides.

Julia Sacher notes, “We discovered that specific regions in the medial temporal lobe, which are pivotal for episodic memory and spatial cognition, undergo changes in size during high estradiol and low progesterone phases. Essentially, these brain areas adapt in sync with the menstrual cycle. Our aim is to investigate whether these rhythmic alterations differ in individuals at risk of memory and mood disorders through subsequent studies.”

She goes on to say, “In the realm of cognitive neuroscience, the female brain remains significantly underexplored. Even though sex steroid hormones wield considerable influence over learning and memory, less than 0.5% of neuroimaging research addresses hormonal transition phases, such as the menstrual cycle, the impact of hormonal contraceptives, pregnancy, and menopause.

Our commitment is to bridge this critical research gap. To uncover the mechanisms behind susceptibility and resilience in mental health disorders like depression or Alzheimer’s disease, a deeper understanding of how the healthy female brain adapts to change is essential.”

Source: Max Planck Society

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