Caffeine's Impact on Sleep: New Study Reveals Age-Dependent Effects on Brain Activity

How does coffee affect a sleeping brain?

Caffeine is not only found in coffee, but also in tea, chocolate, energy drinks and many soft drinks, making it one of the most widely consumed psychoactive substances in the world. In a study published in April in Nature Communications Biology, a team of researchers from Université de Montréal 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 Thölke, 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 with sleep-and-aging 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 organized and flexible. In this state, the brain functions optimally: it can process information efficiently, adapt quickly, learn and make decisions with agility." 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." 40 adults studied To study how caffeine affects the sleeping brain, Carrier's team recorded the nocturnal brain activity of 40 healthy adults using an electroencephalogram. They compared each participant's brain activity on two separate nights -- one when they consumed caffeine capsules three hours and then one hour before bedtime, and another when they took a placebo at the same times. "We used advanced statistical analysis and artificial intelligence to identify subtle changes in neuronal activity," said Thölke, the study's first author. "The results showed that caffeine increased the complexity of brain signals, reflecting more dynamic and less predictable neuronal activity, especially during the non-rapid eye movement (NREM) phase of sleep that's crucial for memory consolidation and cognitive recovery." 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." People in their 20s more affected The study also showed that the effects of caffeine on brain dynamics were significantly more pronounced in young adults between ages 20 and 27 compared to middle-aged participants aged 41 to 58, especially during REM sleep, the phase associated with dreaming. 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. They add that further research is needed to clarify how these neural changes affect cognitive health and daily functioning, and to potentially guide personalized recommendations for caffeine intake.

Study sheds new light on how caffeine can impair sleep and memory recovery

Université de MontréalMay 28 2025 Caffeine is not only found in coffee, but also in tea, chocolate, energy drinks and many soft drinks, making it one of the most widely consumed psychoactive substances in the world. In a study published in April in Nature Communications Biology, a team of researchers from Université de Montréal 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 Thölke, 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 with sleep-and-aging 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. 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." Karim Jerbi, a psychology professor and researcher at Mila - Quebec AI Institute 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." 40 adults studied To study how caffeine affects the sleeping brain, Carrier's team recorded the nocturnal brain activity of 40 healthy adults using an electroencephalogram. They compared each participant's brain activity on two separate nights -- one when they consumed caffeine capsules three hours and then one hour before bedtime, and another when they took a placebo at the same times. "We used advanced statistical analysis and artificial intelligence to identify subtle changes in neuronal activity," said Thölke, the study's first author. "The results showed that caffeine increased the complexity of brain signals, reflecting more dynamic and less predictable neuronal activity, especially during the non-rapid eye movement (NREM) phase of sleep that's crucial for memory consolidation and cognitive recovery." 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." People in their 20s more affected The study also showed that the effects of caffeine on brain dynamics were significantly more pronounced in young adults between ages 20 and 27 compared to middle-aged participants aged 41 to 58, especially during REM sleep, the phase associated with dreaming. 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. They add that further research is needed to clarify how these neural changes affect cognitive health and daily functioning, and to potentially guide personalized recommendations for caffeine intake. Université de Montréal Journal reference: Thölke, P., et al. (2025). Caffeine induces age-dependent increases in brain complexity and criticality during sleep. Communications Biology. doi.org/10.1038/s42003-025-08090-z.

Caffeine Disrupts Sleep Brainwaves and Delays Nighttime Recovery - Neuroscience News

Summary: A new study reveals that caffeine increases the complexity of brain activity during sleep, especially in younger adults, potentially disrupting the brain's ability to recover overnight. Researchers used EEG and AI to analyze sleep in 40 adults after caffeine or placebo intake, identifying less predictable brain signals and increased wake-like brainwave patterns. Caffeine altered deep sleep rhythms by dampening theta and alpha waves while stimulating beta waves linked to alertness. These effects were most pronounced in 20-somethings, likely due to age-related differences in adenosine receptor density, suggesting younger brains are more vulnerable to caffeine's nighttime impact. Caffeine is not only found in coffee, but also in tea, chocolate, energy drinks and many soft drinks, making it one of the most widely consumed psychoactive substances in the world. In a study published in April in Nature Communications Biology, a team of researchers from Université de Montréal 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 Thölke, 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 with sleep-and-aging 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 organized and flexible. In this state, the brain functions optimally: it can process information efficiently, adapt quickly, learn and make decisions with agility." 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." 40 adults studied To study how caffeine affects the sleeping brain, Carrier's team recorded the nocturnal brain activity of 40 healthy adults using an electroencephalogram. They compared each participant's brain activity on two separate nights -- one when they consumed caffeine capsules three hours and then one hour before bedtime, and another when they took a placebo at the same times. "We used advanced statistical analysis and artificial intelligence to identify subtle changes in neuronal activity," said Thölke, the study's first author. "The results showed that caffeine increased the complexity of brain signals, reflecting more dynamic and less predictable neuronal activity, especially during the non-rapid eye movement (NREM) phase of sleep that's crucial for memory consolidation and cognitive recovery." 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." People in their 20s more affected The study also showed that the effects of caffeine on brain dynamics were significantly more pronounced in young adults between ages 20 and 27 compared to middle-aged participants aged 41 to 58, especially during REM sleep, the phase associated with dreaming. 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. They add that further research is needed to clarify how these neural changes affect cognitive health and daily functioning, and to potentially guide personalized recommendations for caffeine intake. Caffeine induces age-dependent increases in brain complexity and criticality during sleep Caffeine is the most widely consumed psychoactive stimulant worldwide. Yet important gaps persist in understanding its effects on the brain, especially during sleep. We analyzed sleep electroencephalography (EEG) in 40 subjects, contrasting 200 mg of caffeine against a placebo condition, utilizing inferential statistics and machine learning. We found that caffeine ingestion led to an increase in brain complexity, a widespread flattening of the power spectrum's 1/f-like slope, and a reduction in long-range temporal correlations. Being most prominent during non-rapid eye movement (NREM) sleep, these results suggest that caffeine shifts the brain towards a critical regime and more diverse neural dynamics. Interestingly, this was more pronounced in younger adults (20-27 years) compared to middle-aged participants (41-58 years) during rapid eye movement (REM) sleep, while no significant age effects were observed during NREM. Interpreting these data in the light of modeling and empirical work on EEG-derived measures of excitation-inhibition balance suggests that caffeine promotes a shift in brain dynamics towards increased neural excitation and closer proximity to a critical regime, particularly during NREM sleep.

How coffee affects a sleeping brain

Caffeine is not only found in coffee, but also in tea, chocolate, energy drinks and many soft drinks, making it one of the most widely consumed psychoactive substances in the world. In a study published in Communications Biology, a team of researchers from Université de Montréal 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 Thölke, 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-aging 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 organized and flexible. In this state, the brain functions optimally: It can process information efficiently, adapt quickly, learn and make decisions with agility." Carrier added, "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." 40 adults studied To study how caffeine affects the sleeping brain, Carrier's team recorded the nocturnal brain activity of 40 healthy adults using an electroencephalogram. They compared each participant's brain activity on two separate nights -- one when they consumed caffeine capsules three hours and then one hour before bedtime, and another when they took a placebo at the same times. "We used advanced statistical analysis and artificial intelligence to identify subtle changes in neuronal activity," said Thölke, the study's first author. "The results showed that caffeine increased the complexity of brain signals, reflecting more dynamic and less predictable neuronal activity, especially during the non-rapid eye movement (NREM) phase of sleep that's crucial for memory consolidation and cognitive recovery." 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." People in their 20s more affected The study also showed that the effects of caffeine on brain dynamics were significantly more pronounced in young adults between ages 20 and 27 compared to middle-aged participants aged 41 to 58, especially during REM sleep, the phase associated with dreaming. 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. 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. They add that further research is needed to clarify how these neural changes affect cognitive health and daily functioning, and to potentially guide personalized recommendations for caffeine intake.

Caffeine at night disrupts sleep and brain activity - Earth.com

Caffeine is woven into daily life, turning up not just in morning coffee but in tea, chocolate, soda, and energy drinks. Yet the same stimulant that keeps billions of people alert may also be changing the way the sleeping brain resets itself overnight, according to new research from the University of Montréal. In a recent study, scientists combined electroencephalography with artificial-intelligence tools to reveal that evening caffeine drives the brain into a more active and less restorative mode during sleep. Researchers also found the effect is most pronounced in people under 30. The research team, led by doctoral trainee Philipp Thölke in the Cognitive and Computational Neuroscience Laboratory (CoCo Lab), recorded the nighttime brain activity of 40 healthy volunteers. Each participant slept in the lab twice: one night after caffeine and another night after placebo, both taken before bed. Throughout the night, electroencephalogram (EEG) electrodes tracked the electrical chatter of neurons, while sophisticated algorithms searched for subtle patterns. "We used advanced statistical analysis and artificial intelligence to identify subtle changes in neuronal activity," Thölke said. His project involved a collaboration with Karim Jerbi, the director of CoCo Lab and a professor of psychology, and sleep-and-aging specialist Julie Carrier. When the researchers compared the caffeine nights with the placebo nights, they saw a clear jump in what neuroscientists call signal complexity. The EEG traces looked more intricate, less predictable, and closer to the patterns typical of wakefulness. The team also measured an increase in "criticality," a concept that Professor Jerbi likens to an orchestra finding its perfect pitch. "Criticality describes a state of the brain that is balanced between order and chaos," he said. "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." Caffeine, he noted, nudges the brain into that same poised, ready-to-learn condition useful at noon, perhaps unwelcome at midnight. "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," Carrier explained. Beyond complexity metrics, the EEG recordings showed noteworthy shifts in traditional sleep rhythms. Under the influence of caffeine, the slow theta and alpha waves crucial for repair and memory were suppressed in non-REM sleep. Meanwhile, faster beta activity, typical of mental engagement while awake, appeared more often. "These changes suggest that even during sleep, the brain remains in a more activated, less restorative state under the influence of caffeine," Jerbi said. The volunteers ranged from 20 to 58 years old, allowing the team to see how age influences caffeine's punch. Young adults from 20 to 27 exhibited the strongest boost in criticality and the greatest suppression of slow waves, especially during REM sleep. That age skew likely stems from biology. Youngsters have more adenosine receptors in the brain, giving caffeine - an adenosine blocker - extra leverage. "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. Taken together, the findings suggest that an after-dinner espresso may not only delay sleep but also reduce its quality. For students and young professionals who lean on late-day lattes, the data raise particular concerns, since their brains appear most sensitive. Yet the study's authors are cautious about sweeping prescriptions. They note that caffeine's popularity - consumed by an estimated 80 percent of adults worldwide - makes nuanced guidance essential. Future work will need to unravel how the observed neural changes translate into next-day performance, long-term cognitive health, and individual differences tied to genetics or existing sleep disorders. Still, the research shows that sleep is not simply unconscious downtime. The brain finely tunes its overnight choreography, and stimulants can shift its rhythm. As the researchers continue to explore how common substances alter criticality and complexity, they hope to inform personalized recommendations. This could help coffee lovers balance the perks of daytime alertness with the necessity of deep, restorative sleep. Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

How Does Coffee Affect a Sleeping Brain? | Newswise

AI-generated image of a person undergoing polysomnographic recordings with EEG electrodes during sleep, created using DALL·E for illustrative purposes / Prompt by Karim Jerbi Newswise -- Caffeine is not only found in coffee, but also in tea, chocolate, energy drinks and many soft drinks, making it one of the most widely consumed psychoactive substances in the world. In a study published in April in Nature Communications Biology, a team of researchers from Université de Montréal 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 Thölke, 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 with sleep-and-aging 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 organized and flexible. In this state, the brain functions optimally: it can process information efficiently, adapt quickly, learn and make decisions with agility." 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." 40 adults studied To study how caffeine affects the sleeping brain, Carrier's team recorded the nocturnal brain activity of 40 healthy adults using an electroencephalogram. They compared each participant's brain activity on two separate nights -- one when they consumed caffeine capsules three hours and then one hour before bedtime, and another when they took a placebo at the same times. "We used advanced statistical analysis and artificial intelligence to identify subtle changes in neuronal activity," said Thölke, the study's first author. "The results showed that caffeine increased the complexity of brain signals, reflecting more dynamic and less predictable neuronal activity, especially during the non-rapid eye movement (NREM) phase of sleep that's crucial for memory consolidation and cognitive recovery." 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." People in their 20s more affected The study also showed that the effects of caffeine on brain dynamics were significantly more pronounced in young adults between ages 20 and 27 compared to middle-aged participants aged 41 to 58, especially during REM sleep, the phase associated with dreaming. 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. They add that further research is needed to clarify how these neural changes affect cognitive health and daily functioning, and to potentially guide personalized recommendations for caffeine intake. About this study "Caffeine induces age-dependent increases in brain complexity and criticality during sleep," by Philipp Thölke et al., was published April 30, 2025 in Nature Communications Biology.

How Caffeine Affects Your Brain While You Sleep

SUNDAY, June 1, 2025 (HealthDay News) -- Your morning cup of coffee might help you power through the day -- but could it be keeping your brain too alert at night, even while you sleep? A new study suggests that caffeine doesn't just affect your energy levels. It may also change how your brain functions during sleep, especially in 20-somethings. Researchers in Canada found that drinking caffeine before bed may keep the brain in a more active state overnight, a news release shows. Published in the journal Nature Communications Biology, the study used electroencephalography (EEG) and artificial intelligence to examine how caffeine changes the brain's behavior during rest. "We used advanced statistical analysis and artificial intelligence to identify subtle changes in neuronal activity," said lead author Philipp Thölke, a research trainee at the University of Montreal. "The results showed that caffeine increased the complexity of brain signals, reflecting more dynamic and less predictable neuronal activity, especially during the non-rapid eye movement (NREM) phase of sleep that's crucial for memory consolidation and cognitive recovery," he said in a news release. Researchers found that caffeine increased the complexity of brain signals. It also boosted something known as "criticality." "Criticality describes a state of the brain that is balanced between order and chaos," said study co-author Karim Jerbi, a University of Montreal psychology professor and director of its Cognitive and Computational Neuroscience Lab. "In this state, the brain functions optimally," he said in a news release. "It can process information efficiently, adapt quickly, learn and make decisions with agility." But during sleep, that same alert state isn't exactly ideal. "Caffeine stimulates the brain and pushes it into a state of criticality, where it is more awake, alert and reactive," study co-leader Julie Carrier, director of the Canadian Sleep and Circadian Network, explained in a news release. "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." To study these effects, researchers observed 40 healthy adults as they slept. Participants took either caffeine capsules or placebos on different nights, three hours before bedtime, and then one hour before bedtime. The researchers found that caffeine increased beta brain waves -- usually associated with mental engagement and wakefulness -- and weakened slower brain waves like theta and alpha, which are tied to deep and restorative sleep. "These changes suggest that even during sleep, the brain remains in a more activated, less restorative state under the influence of caffeine," Jerbi said. "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," he addd. The impact of caffeine was especially strong in 20- to 27-year-olds, compared to middle-aged adults between 41 and 58. This difference may be due to changes in adenosine receptors in the brain. Adenosine is a chemical that builds up throughout the day, making you feel sleepy. Caffeine blocks adenosine receptors to keep you awake -- but younger adults have more of these receptors, so the stimulant has a stronger effect. "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. Since caffeine is so widely used -- especially as a daily solution for fatigue -- researchers said further study is needed to understand its long-term effects on brain health and to guide personalized recommendations for different age groups.

Super common habit is keeping your brain awake while you sleep -- ...

Late-night scrolling isn't the only thing sabotaging your slumber. New research suggests that a common daily habit may send your brain into overdrive while you sleep -- even if you do it hours before bedtime. Scientists warn the disruption could interfere with the brain's overnight recovery processes, potentially taking a toll on your cognitive health. In the study, Canadian researchers had 40 healthy adults spend two nonconsecutive nights in a sleep lab. On one night, participants consumed 200 milligrams of caffeine -- the equivalent of about two cups of coffee -- a few hours before bed. On the other, they were given a placebo. While most people know caffeine can make it harder to fall asleep, researchers used EEG scans to track brain activity after participants dozed off and found it kept their brains in a heightened state of alertness long after they shut their eyes. They found, for the first time, that the stimulant pushed the brain into a state of "criticality," making it more awake, alert and reactive than it should be while catching Zzz's. "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," said Dr. Julie Carrier, a psychology professor at the University of Montreal and co-author of the study. The team used artificial intelligence to detect subtle changes in neuronal activity and found that caffeine increased the complexity of brain signals, preventing the brain from fully powering down during sleep. The effect was especially strong during non-REM sleep -- the deep stage critical for memory and cognitive recovery. Researchers also observed changes in brain wave patterns. Slow waves linked to deep, restorative rest were reduced, while faster waves associated with wakefulness and mental activity increased. "These changes suggest that even during sleep, the brain remains in a more activated, less restorative state under the influence of caffeine," said Dr. Karim Jerbi, a psychology professor at the University of Montreal and researcher at the Mila Quebec Artificial Intelligence Institute, who co-authored the study. "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," he added. Notably, the stimulant's effect's were far more pronounced in participants aged 20 to 27 compared to those aged 41 to 58 -- especially during REM sleep, the dreaming phase tied to emotional and cognitive processing. Researchers believe younger adults responded more strongly due to having more adenosine receptors. These molecules gradually accumulate in the brain throughout the day, triggering 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. The findings suggest younger brains may be especially vulnerable to caffeine's hidden impact on rest. Caffeine is the most widely consumed psychoactive drug in the world, commonly found in products such as coffee, tea, chocolate, sodas and energy drinks. A 2023 Sleep Foundation survey found that 94% of US adults consume caffeinated beverages, and 64% drink them daily. Of those, 40% said they didn't think it affected their sleep. While the FDA says up to 400 milligrams of caffeine per day is generally safe for healthy adults, the study suggests it could still be interfering with sleep quality -- even hours after your last sip. The scientists are calling for further research exploring how these nighttime brain changes affect day-to-day functioning and cognitive health. This, they said, could one day shape personalized caffeine recommendations.