A groundbreaking study from the University of California, Santa Barbara, has revealed that men’s brains shrink throughout the day, a process tied to daily hormonal fluctuations. These findings challenge previous assumptions that hormone-driven brain changes were exclusive to women.
The research focused on one male participant whose brain was scanned 40 times over a 30-day period. According to the study, the overall volume of the brain shrank by 8pm each day and grew back overnight. This shrinking was most noticeable in areas of the brain responsible for visual and sensory processing.
Testosterone, cortisol, and estradiol—three key steroid hormones—were found to peak in the morning and decline as the day progressed. “You can think of it almost like a pulsating rhythm,” said Laura Pritschet, one of the study’s authors. The reduction in brain size coincided with this hormonal decline, suggesting a possible connection between the two.
Interestingly, the cortex, which controls important functions such as memory and emotions, also thinned over the course of the day, with gray matter volume dropping by an average of 0.6%. While this shrinkage may seem small, it could still impact cognitive functions, though researchers are not yet certain if hormones directly cause these changes.
Elle Murata, another researcher involved in the study, noted that while the study supports the theory that hormones influence brain structure, more research is needed. “This is another example debunking the myth that hormones are only relevant for females,” Murata said.
The study’s findings offer new insight into how men’s brains respond to daily hormonal shifts, but with only one participant, researchers caution against generalizing the results. Future studies are expected to explore the effects of sleep and stress on brain volume.
