Caffeine, a common psychoactive substance found in coffee, tea, chocolate, energy drinks, and sodas, is widely consumed around the globe. Recent research has shed new light on how caffeine influences sleep and brain recovery, both physical and cognitive, during the night.
A study led by Philipp Thölke, a research trainee at Université de Montréal’s Cognitive and Computational Neuroscience Laboratory (CoCo Lab), and co-led by Professor Karim Jerbi, director of the lab, explores the complex effects of caffeine on sleep. The research team also included Julie Carrier, a professor specializing in sleep and aging psychology, and her colleagues at the Centre for Advanced Research in Sleep Medicine.
Using artificial intelligence (AI) and electroencephalography (EEG), the researchers studied how caffeine impacts brain activity during sleep. Their findings revealed that caffeine boosts the complexity of brain signals and enhances brain “criticality” during sleep, a phenomenon more pronounced in younger adults.
Understanding Criticality in the Brain
“Criticality refers to a state where the brain is in balance between order and chaos,” explained Jerbi. “It’s like an orchestra—too quiet and nothing happens, too chaotic and there’s noise. Criticality is the sweet spot where the brain is organized yet flexible, allowing it to process information efficiently, adapt quickly, and make decisions effectively.”
Carrier noted that while caffeine helps the brain stay alert and reactive during the day, this heightened state could interfere with rest at night. “Caffeine pushes the brain into a state of criticality, which is useful for focus but may prevent the brain from properly relaxing and recovering during sleep,” she said.
The Study and Its Findings
In the study, the team recorded the brain activity of 40 healthy adults using EEG over two nights. On one night, participants consumed caffeine capsules three hours and one hour before sleep; on the other, they took a placebo. The researchers applied advanced AI and statistical analysis to examine subtle changes in brain activity.
The results showed that caffeine increased the complexity of brain signals, reflecting more dynamic and unpredictable neuronal activity. This change was especially noticeable during the non-rapid eye movement (NREM) phase of sleep, which is vital for memory consolidation and cognitive recovery.
The team also observed significant changes in the brain’s electrical rhythms during sleep. Caffeine reduced slower brain waves, such as theta and alpha waves, which are associated with deep, restorative sleep. In contrast, it stimulated beta wave activity, typically seen when the brain is awake and engaged in mental tasks.
“This shift in brain rhythms suggests that caffeine keeps the brain in a more active state, even during sleep,” said Jerbi. “As a result, the brain may not fully relax or recover, which could impact memory processing.”
Young Adults Are More Affected by Caffeine
The study also found that the effects of caffeine were more pronounced in younger adults, particularly those aged 20 to 27, compared to older participants aged 41 to 58. This effect was especially evident during REM sleep, the phase most closely associated with dreaming.
Young adults are more sensitive to caffeine due to a higher density of adenosine receptors in their brains. Adenosine is a molecule that builds up throughout the day and causes feelings of fatigue. As people age, the number of these receptors decreases, reducing caffeine’s ability to block adenosine and enhance brain activity.
“These age-related differences suggest that younger brains are more affected by caffeine, which may explain why older individuals experience less of the stimulant’s impact,” Carrier said.
Implications for Caffeine Consumption
Given caffeine’s widespread use as a remedy for fatigue, particularly among young adults, the research highlights the need for a deeper understanding of how it affects brain function across different age groups. The researchers emphasize the importance of investigating these effects further, particularly in relation to cognitive health and daily functioning.
“More research is needed to explore how caffeine-induced changes in brain activity impact overall health, and to develop personalized recommendations for caffeine intake,” the team concluded.
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