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Caffeine induces age-dependent increases in brain complexity and criticality during sleep
Caffeine isn’t just in your morning coffee. It’s also in tea, chocolate, energy drinks, and many popular soft drinks, making it one of the most widely consumed psychoactive substances around the globe. Now, new research from the University of Montreal reveals how caffeine might be doing more than just keeping you awake. In a study published in Communications Biology, scientists discovered that caffeine can actually change how the brain recovers overnight, affecting both physical restoration and cognitive function.
They showed for the first time that caffeine increases the complexity of brain signals and enhances brain “criticality” during sleep. Interestingly, this was more pronounced in younger adults.
“Criticality describes a state of the brain that is balanced between order and chaos,” said Jerbi. “It’s like an orchestra: too quiet and nothing happens, too chaotic and there’s cacophony. Criticality is the happy medium where brain activity is both organized and flexible. In this state, the brain functions optimally: it can process information efficiently, adapt quickly, learn, and make decisions with agility.”
The researchers also discovered striking changes in the brain’s electrical rhythms during sleep: caffeine attenuated slower oscillations such as theta and alpha waves, generally associated with deep, restorative sleep, and stimulated beta wave activity, which is more common during wakefulness and mental engagement.
“These changes suggest that even during sleep, the brain remains in a more activated, less restorative state under the influence of caffeine, Young adults showed a greater response to caffeine, likely due to a higher density of adenosine receptors in their brains. Adenosine is a molecule that gradually accumulates in the brain throughout the day, causing a feeling of fatigue.
“Adenosine receptors naturally decrease with age, reducing caffeine’s ability to block them and improve brain complexity, which may partly explain the reduced effect of caffeine observed in middle-aged participants,” Carrier said.
And these age-related differences suggest that younger brains may be more susceptible to the stimulant effects of caffeine. Given caffeine’s widespread use around the world, especially as a daily remedy for fatigue, the researchers stress the importance of understanding its complex effects on brain activity across different age groups and health conditions.
Ref:
Thölke, P., Arcand-Lavigne, M., Lajnef, T. et al. Caffeine induces age-dependent increases in brain complexity and criticality during sleep. Commun Biol 8, 685 (2025). https://doi.org/10.1038/s42003-025-08090-z
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