A recent month-long study has revealed that a man’s brain volume consistently shrinks from morning to night, then resets overnight. The study suggests that the daily fluctuations in male hormones, such as testosterone, cortisol, and estradiol, might contribute to this change. Scans of a 26-year-old male’s brain over 30 days showed a 0.6% reduction in overall brain volume by evening, with the most noticeable shrinkage occurring in the cortex, which is responsible for complex cognitive functions. The occipital and parietal cortices, involved in visual processing and sensory information, shrank the most, alongside changes in deeper structures like the cerebellum and hippocampus.
The research, which scanned the brain at either 7 a.m. or 8 p.m., highlights the significant drop in steroid hormones—around 70% from morning to evening. This rhythmic cycle of hormones, known as the circadian rhythm, might influence these daily brain changes. However, researchers stress that it’s still unclear if the hormone fluctuations directly cause the brain’s shrinkage.
While similar fluctuations occur in females, their effects are less pronounced due to the influence of the menstrual cycle, which drives longer-term hormonal shifts. This study adds to a growing body of research that challenges the misconception that hormonal cycles predominantly affect women.
Interestingly, the study also found changes in brain connectivity that follow the same daily rhythm. The brain’s synchronization, or “coherence,” fluctuates in tandem with hormone levels, particularly in regions responsible for visual processing.
Though these results come from a single participant, they raise questions about the broader impacts of daily hormonal cycles on brain structure and function. The researchers hope to further investigate how sleep, which is critical for brain health, might interact with these patterns.
