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A Canadian study using AI and EEG shows caffeine disrupts brain recovery during sleep by increasing neural complexity and altering rhythms. These effects, especially during REM sleep, are more intense in younger adults than older ones.
An AI-powered study has uncovered how caffeine affects the brain even after you fall asleep and it’s a wake-up call for coffee lovers.
While coffee is known to boost alertness during the day, researchers at the Université de Montréal have found that caffeine doesn’t fully let go of your brain at night. Instead, it interferes with the brain’s 'criticality' which is a delicate balance between order and chaos that’s essential for restful, restorative sleep.
Groundbreaking research from Université de Montréal
In a study published in April in Nature Communications Biology, a team of researchers from Université de Montréal examined how caffeine affects the brain’s ability to recover overnight, both physically and cognitively.
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The research was led by Philipp Tholke, a trainee at the university's Cognitive and Computational Neuroscience Laboratory (CoCo Lab), and co-led by psychology professor Karim Jerbi, also a researcher at Mila, Quebec AI Institute.
Working with sleep-and-ageing expert Julie Carrier and her team at the Centre for Advanced Research in Sleep Medicine, they applied artificial intelligence and electroencephalography (EEG) to study caffeine's impact on sleep quality.
Caffeine increases brain signal complexity and ‘criticality’
They showed for the first time that caffeine increases the complexity of brain signals and enhances brain "criticality" during sleep, an effect 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 organised and flexible. In this state, the brain functions optimally: it can process information efficiently, adapt quickly, learn and make decisions with agility," he added.
Brain stays alert, not fully resting
"Caffeine stimulates the brain and pushes it into a state of criticality, where it is more awake, alert and reactive. While this is useful during the day for concentration, this state could interfere with rest at night: the brain would neither relax nor recover properly."
Caffeine alters sleep rhythms, blocks deep rest
The researchers also observed major changes in the brain's electrical rhythms during sleep. Caffeine reduced slower waves such as theta and alpha, typically associated with deep and restorative sleep, and increased beta wave activity, which is usually linked to wakefulness and active thinking.
"These changes suggest that even during sleep, the brain remains in a more activated, less restorative state under the influence of caffeine," said Jerbi.
"This change in the brain's rhythmic activity may help explain why caffeine affects the efficiency with which the brain recovers during the night, with potential consequences for memory processing."
Young adults more affected than older adults
The study also found that caffeine's effects on brain dynamics were much stronger in young adults aged 20 to 27 than in middle-aged adults aged 41 to 58. This was especially evident during REM sleep, the stage most closely linked with dreaming.
-With agency inputs
