Key Points

In a study published in April in Nature Communications Biology, a team of researchers from Universite de Montreal shed new light on how caffeine can modify sleep and influence the brain's recovery -- both physical and cognitive -- overnight.

The research was led by Philipp Tholke, a research trainee at UdeM's Cognitive and Computational Neuroscience Laboratory (CoCo Lab), and co-led by the lab's director Karim Jerbi, a psychology professor and researcher at Mila -- Quebec AI Institute.

Working with sleep-and-ageing psychology professor Julie Carrier and her team at UdeM's Centre for Advanced Research in Sleep Medicine, the scientists used AI and electroencephalography (EEG) to study caffeine's effect on sleep.

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 organised and flexible. In this state, the brain functions optimally: it can process information efficiently, adapt quickly, learn and make decisions with agility," added Jerbi.

Added Carrier: "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."

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," says Jerbi, who also holds the Canada Research Chair in Computational Neuroscience and Cognitive Neuroimaging. "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."

The study also showed that the effects of caffeine on brain dynamics were significantly more pronounced in young adults between the ages of 20 and 27 compared to middle-aged participants aged 41 to 58, especially during REM sleep, the phase associated with dreaming.

- ANI