Scientists have found that brief patterns of brain activity normally seen during deep sleep frequently intrude into the waking hours of adults with attention-deficit hyperactivity disorder. This phenomenon tends to explain why people with this condition often experience decreased alertness and excessive daytime sleepiness. The survey results are neuroscience journalprovides evidence that attention deficit hyperactivity disorder may be deeply connected to how the brain regulates the boundaries between sleep and wakefulness.
Adults with Attention Deficit Hyperactivity Disorder often face challenges with staying focused, behavioral variability, and impulsivity. They also tend to report higher rates of sleep disturbances and daytime fatigue than the general population. This combination of symptoms led researchers to wonder if there might be a physical overlap between the sleep and attention systems in the brain.
“My interest arose from previous work looking at how drugs like methylphenidate (MPH, commonly known as Ritalin) affect waking slow waves in neurotypical patients,” explained Monash University researcher Elaine Pingal. “What intrigued me was how MPH is commonly used to treat both narcolepsy and ADHD, which are ostensibly very different conditions.”
When study results showed that this drug reduced the occurrence of these slow waves, the question arose whether slow waves during wakefulness played a meaningful role in this condition. Thomas Andrillon, a researcher at the Paris Brain Institute and lead author of the study, recognizes the potential of this idea. “Thomas was the one who first had the vision to bring this question to the ADHD clinical population, and it was an honor to be part of this study,” Pingal said.
To investigate this, scientists recruited 63 young people with an average age of 23. The sample included 32 adults with a formal diagnosis of attention-deficit/hyperactivity disorder and 31 typically developing adults without attention-deficit/hyperactivity disorder. Participants with this disorder were asked to stop taking their standard medication 72 hours before the experiment to ensure that their brain activity was measured without the medication.
During the experiment, participants completed a computer-based task designed to test sustained attention for 52 minutes. Numbers 1 through 9 flashed continuously on the screen. Participants were instructed to press all numbered buttons except number 3 as quickly as possible. This repetitive activity required constant vigilance and the ability to suppress impulsive reactions.
While the participants completed the task, the researchers continuously recorded their brain activity using electroencephalograms. This involves placing a cap with 64 special sensors on the scalp to measure electrical signals in the brain. The scientists specifically looked for high-amplitude slow waves, which indicate that local parts of the brain are temporarily slowing down and entering a sleep-like state.
“Sleep wave intrusion is a very normal phenomenon. Think of a long distance run. After a while, physical fatigue forces you to take a break. The same applies to mental fatigue,” Andrilon explained. “After a day of waking up, or a poor night’s sleep, the brain also takes a break in the form of slow waves.”
Pingal agreed, noting that the brain temporarily goes offline for local recovery. “The first thing I want people to know is that slow waves of sleep-like wakefulness are not unique to people with ADHD; they happen to everyone,” Pingal told PsyPost. “The more tired you are or the longer you’ve been working, the more likely you are to experience these symptoms.”
However, this study found differences in the frequency of these events. “These brief periods of decreased brain activity occur in anyone, but they occur more frequently in people with ADHD,” Andrilon added. “Our findings suggest that this may be an important brain mechanism that explains the difficulty in maintaining stable attention and performance over long periods of time.”
Every 40 to 70 seconds, the computer task was paused and participants were asked what they were thinking just before the interruption. They may report symptoms such as not being actively on task, having a wandering mind, feeling blank, or not remembering. Mind wandering involves thinking about personal matters or distractions that are unrelated to work. Mind blanking refers to the moment when conscious thought becomes completely empty.
Behavioral results showed clear differences in performance between the two groups. Adults with Attention Deficit Hyperactivity Disorder make significantly more commission errors, which means they press buttons more often when they should be holding back. Their reaction times also varied much more from one moment to the next than the neurotypical group, reflecting fluctuations in their level of attention.
“There were a few things that stood out, one of which was around mind wandering. In the neurotypical participants, mind wandering was reported to be more deliberate, like intentional mental breaks,” Pingal noted. “However, participants with ADHD reported more unintentional mind wandering, meaning their attention just happened without them choosing to divert their attention.”
Pingal also highlighted an unexpected finding regarding fatigue. “Another surprising finding was around sleepiness. If you have ADHD and struggle with sleep, it might be a natural assumption that you’ll feel more tired throughout the day,” Pingal said.
“But in our cohort, we actually found no difference in daytime sleepiness between the two groups,” she continued. “What was different was that participants with ADHD felt more sleepy during the task itself, suggesting that they are not sleepy people in general, and their brains may fatigue more quickly under sustained effort. That said, this is one cohort, and further research is definitely needed before broader conclusions can be drawn.”
Recordings of brain activity provided evidence to explain these behavioral differences. “Adults with ADHD have a significantly higher density of slow waves, which are typically observed during deep sleep,” Andrilon said. “These waves are not trivial. The denser the waves, the more likely it is that participants will make careless mistakes that will slow down their reaction times or change their reaction times.”
To understand the relationship between medical diagnoses, brain activity, and performance, researchers used a statistical tool called mediation analysis. This technique tests whether intermediate variables explain the association between the initiating factor and the outcome. This analysis suggests that the increased presence of arousal slow waves is the primary physical mechanism driving the attentional difficulties seen in this condition.
Because of this strong association, tracking these brain patterns may have clinical utility. “These local sleep waves could be important diagnostic biomarkers,” Andrilon said.
Although the study provides a detailed neurophysiological explanation of attention difficulties, the scientists acknowledge some limitations. “Replication of these findings, larger and more diverse cohorts, longer studies, and a clearer picture of the underlying mechanisms will be needed before any of these can responsibly inform real-world treatments,” Pingal explained.
“Also, we cannot yet say whether ADHD makes it harder to sleep or whether sleep deprivation causes ADHD symptoms,” Pingal cautioned. “These two probably influence each other, but long-term studies are needed to clarify the direction of causality. Our findings indicate that slow waves during wakefulness are a potential source of decreased attention, but how this relates to sleep more broadly remains to be established.”
“An interesting next step in this area of research is the use of auditory stimulation during sleep,” Pingal added. “This involves stimulating slow wave activity during sleep by playing a quiet sound that coincides with the rise of slow waves. This approach has shown promising results in boosting activity in people who respond to slow waves, and has been shown to improve memory and cognition.”
“Although the mechanism is not yet fully understood, the idea is that by enhancing slow waves during sleep, the brain may reduce the need to generate slow waves during wakefulness,” Pingal concluded. “This is probably just one piece of a larger puzzle, but it’s a promising avenue, and studies of slow waves in wakes could help clarify the picture.”
The study, “Sleep-like slow waves during wakefulness mediate attention and vigilance difficulties in adult attention-deficit/hyperactivity disorder,” was authored by Elaine Pingal, James Jackson, Anikó Kusztor, David Chapman, Jennifer Windt, Sean PA Drummond, Tim J. Silk, Mark A. Bellgrove, and Thomas Andrillon.
