Our brains are constantly changing, and a new study suggests that the daily ebb and flow of hormones in men might play a significant role in this process. The research, conducted by scientists at the University of California, Santa Barbara, indicates that brain volume shrinks throughout the day, only to recover overnight, creating a cyclical pattern.
The study, published in The Journal of Neuroscience, involved meticulously scanning the brain of a 26-year-old male participant 40 times over 30 days. Each magnetic resonance imaging (MRI) scan was taken at either 7 a.m. or 8 p.m., aligning with the peak and trough of steroid hormone levels – namely, testosterone, cortisol, and estradiol.
The researchers observed a marked decrease in brain volume throughout the day, accompanied by a reduction in the thickness of the cortex, the brain’s outer layer. Gray matter, which houses the cell bodies of neurons and their connections, experienced an average decrease of about 0.6%.
Interestingly, the occipital and parietal cortices, regions associated with visual processing and spatial awareness, showed the most significant shrinkage. Changes were also noted in deeper brain structures, including the cerebellum (coordinating movement), brainstem (relaying information between the brain and body), and parts of the hippocampus (memory storage).
The observed brain volume decline mirrors the daily decrease in steroid hormone levels, raising the question of whether these hormonal fluctuations directly influence brain structure. While the study doesn’t definitively establish a causal link, it underscores the potential significance of hormones in shaping brain dynamics.
The study’s lead author, Laura Pritschet, now a postdoctoral scholar at the University of Pennsylvania Perelman School of Medicine, emphasizes that this research challenges the misconception that hormonal variability is primarily relevant to women.
The findings align with previous studies demonstrating the influence of steroid hormones on brain structure. For instance, the menstrual cycle has been linked to brain volume changes, and studies suggest these changes are absent when the hormonal cycle is altered by methods like birth control.
Furthermore, decades of animal research have indicated that steroid hormones play a role in shaping brain structure on short timescales. While the current study can’t definitively claim that hormones directly cause the observed brain shrinkage, it strengthens the understanding of their potential impact.
The research also highlights the intriguing possibility that the daily fluctuations in brain connectivity, observed in a separate study by the same team, may be linked to the hormonal cycle. This separate study, focusing on communication patterns between different brain regions, revealed a synchronized rhythm in brain activity that corresponded with steroid hormone levels.
The study’s participant, Pavel Shapturenka, shared his perspective on the research. He highlighted the importance of understanding hormonal variability in men, given its potential implications for brain function.
The researchers, Pritschet and Elle Murata, a doctoral student at UCSB, emphasize that further investigation is needed to understand the interplay between sleep, hormonal fluctuations, and brain structure.
This study opens a new avenue of research into the dynamic relationship between hormones, brain structure, and cognitive function. It serves as a reminder that the brain is a remarkably adaptable organ, constantly responding to internal and external cues, including the rhythmic ebb and flow of our hormones.
