Study Finds Men’s Brains Shrink And Grow Throughout The Day

A recent study conducted by researchers at the University of California, Santa Barbara, reveals that men’s brains shrink throughout the day. This discovery sheds light on how hormones play a role in brain size fluctuations, which are tied to daily hormonal cycles.

The study, published in The Journal of Neuroscience, focused on a 26-year-old man whose brain was scanned 40 times over the course of 30 days. The results showed that by evening, the overall brain volume had decreased, particularly in areas responsible for sensory and visual processing. The brain resets overnight, growing back to its original size by the morning.

Researchers linked this pattern of brain shrinkage and regrowth to changes in levels of key hormones. Testosterone, estradiol, and cortisol—all steroid hormones—were found to follow a daily rhythm, with peak levels in the morning and a sharp decline by evening. “Males show this 70% decrease from morning to night in steroid hormones,” said study co-author Laura Pritschet.

Interestingly, this study challenges the common belief that hormones only play a significant role in women’s biology. While women’s hormones fluctuate over a menstrual cycle, men experience notable hormonal shifts within a single day, which may influence brain function.

However, researchers are not yet able to confirm whether the hormones directly cause the changes in brain volume. “We can’t say that it’s directly causing it,” admitted study co-author Elle Murata, though she emphasized the importance of hormones in the brain’s structure.

The research also found that the cortex, the brain’s outer layer, became thinner by 8pm each day, with gray matter volume falling by about 0.6% on average. Gray matter plays a crucial role in memory, movement, and emotions, meaning these fluctuations could impact cognitive functions.

This study offers new insight into how men’s hormonal cycles might affect brain function throughout the day, though it is important to note that the study’s findings are based on only one participant. Future studies may investigate how sleep and other factors influence brain changes.