New research reveals that caffeine doesn’t stop working when you fall asleep — it continues altering your brain’s activity, particularly in young adults.
Key Points at a Glance
- Caffeine increases brain signal complexity and criticality even during sleep
- It alters deep-sleep brainwaves, possibly impairing nighttime recovery
- Younger adults are more affected due to higher adenosine receptor density
- AI and EEG helped uncover these subtle nighttime neural changes
We reach for coffee to stay sharp, focused and alert. But what happens when the buzz lingers into the night? A team of neuroscientists from Université de Montréal used artificial intelligence and high-resolution EEG data to find out. Their surprising discovery: caffeine continues stimulating the brain even after we’ve drifted into sleep, subtly reshaping how our minds recover overnight.
Led by Philipp Thölke and Karim Jerbi at UdeM’s Cognitive and Computational Neuroscience Laboratory, the study was co-conducted with sleep expert Julie Carrier and her team at the Centre for Advanced Research in Sleep Medicine. Published in Nature Communications Biology, the research focused on understanding caffeine’s influence on “criticality” — a delicate, optimal balance in brain activity that enables complex processing and adaptability.
“Think of criticality as an orchestra in perfect harmony,” explains Jerbi. “Too little stimulation and nothing happens. Too much, and it’s pure chaos. At criticality, the brain functions at its best.”
Caffeine pushes the sleeping brain closer to this stimulated, alert state — a useful adaptation during waking hours, but potentially disruptive at night. The researchers tested 40 healthy adults, analyzing their brainwaves on nights with and without caffeine using EEG. The results showed heightened complexity in brain signals, especially during the non-REM phase crucial for cognitive restoration. Notably, beta waves — typically linked to alertness — increased, while slower, restorative waves like alpha and theta weakened.
This phenomenon was especially pronounced in participants aged 20 to 27. According to Carrier, this is likely due to their higher density of adenosine receptors, which caffeine targets. Adenosine naturally builds up during the day to trigger fatigue — caffeine works by blocking this effect.
“As we age, we lose some of these receptors,” Carrier noted, “which may explain the diminished impact in older participants.”
Despite caffeine’s daily role as a fatigue-fighter, the study raises questions about its broader neurological effects. Could evening coffee be stealthily undermining sleep quality and brain recovery, particularly in younger users? The authors suggest further studies to explore how long-term caffeine use impacts memory, cognitive health and sleep architecture across different age groups.
“Understanding these nuances helps guide more personalized caffeine recommendations,” Thölke said. “Sleep isn’t just about resting — it’s a time when the brain reorganizes and repairs. Caffeine may be keeping parts of it too awake to do that properly.”
With sleep quality increasingly recognized as a cornerstone of mental and physical health, this research offers a timely insight into one of the world’s most consumed — and misunderstood — substances.
Source: Université de Montréal
