Men's brains shrink in the evening and reset overnight

The human brain is a marvel of biological adaptation with processes that continue to astonish us. Have you ever noticed how your brain changes, affecting your attention span or mental function as the day progresses?

A fascinating study from the University of California, Santa Barbara (UCSB) sheds light on this phenomenon, and the findings are truly amazing.

Changes in the male brain

In a unique endeavor, researchers monitored the brain of a 26-year-old man over 30 consecutive days.

The findings? The male brain experiences a pulsating rhythm throughout the day, with a noticeable decrease in overall volume and cortical thickness by 8 p.m.

This nightly shrinkage, however, is not permanent, with the brain seemingly resetting overnight.

Do hormones cause the brain shrink?

This surprising pattern in the brain seems to have company. Rising and falling levels of three steroid hormones – testosterone, cortisol, and estradiol – coincide with the daily pattern.

You might imagine that this rhythm is exclusive to men, but the experts noted that this is not the case.

Study co-author Laura Pritschet, a postdoctoral scholar at the University of Pennsylvania Perelman School of Medicine, explained that women also witness daily hormonal fluctuations.

However, the menstrual cycle can mask these changes due to its longer-term shifts in hormones.

Grey matter in the brain

The researchers also noted changes in the volume of grey matter, a critical component involved in mental functions, emotions, and movement. As the evening set in, the average grey matter volume fell by about 0.6 percent.

Two specific regions in the brain’s cortex – the occipital and parietal cortices involved in sensory and visual processing – were found to shrink the most, adding curious detail to this phenomenon.

Deeper changes in the brain

Not just the cortex, but deeper structures in the brain like the cerebellum, brainstem, and parts of the hippocampus also fluctuated throughout the day.

The affected regions are responsible for movement coordination, information relay, and memory storage, which means that changes in these brain structures potentially affect a multitude of daily functions.

The question that begs to be asked at this point is, do steroid hormones trigger these changes in the brain structure? So far, the researchers are not entirely sure.

Elle Murata, study co-author and doctoral student at UCSB, is convinced that hormones play a role in the observed brain changes. “But in this study, we can’t say that it’s directly causing it.”

Broadening the hormonal horizon

Murata noted that the study further debunks the myth that hormones are relevant only to females.

“All the information that’s out there highlights the inherent endocrine (hormonal) variability in women,” said Pavel Shapturenka, whose brain was scanned for the study.

“I like the counterpoint that we are now highlighting the ways in which men’s endocrine systems are variable.”

Circadian rhythms and the shrinking brain

The interplay between the brain’s physiological changes and the body’s circadian rhythms is a profound area of exploration in neuroscience.

The circadian clock regulates various bodily functions, ensuring that physiological processes are aligned with the 24-hour day-night cycle.

The observed shrinkage and expansion of the brain’s structures throughout the day could be linked to circadian cycles, suggesting that the brain is finely tuned to external time cues.

This connection points to the potential impact these rhythmic changes have on cognitive performance, alertness, and even mood.

Understanding this synchronization may eventually shed light on optimizing mental and physical health by aligning lifestyles with these natural rhythms.

Implications for health and well-being

The findings from the study hold significant implications for health and well-being, particularly concerning mental health and cognitive disorders.

As hormonal fluctuations and brain volume changes can influence mood, identifying individuals who might exhibit atypical patterns could help in early diagnosis and intervention for conditions like depression or anxiety.

Furthermore, these insights could pave the way for more personalized medicine approaches, where treatments are tailored to an individual’s unique hormonal and brain pattern profiles.

Future research directions

Investigating whether lifestyle factors, such as diet, exercise, or sleep, can mitigate or exacerbate daily brain changes may open new frontiers in promoting holistic health.

While the findings are certainly intriguing, they stem from monitoring a single individual and cannot conclusively represent the wider population.

Going forward, the researchers plan to investigate the influence of sleep variances on the brain.

The study is published in The Journal of Neuroscience.

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