ADHD: towards a role of local sleep in attention disorders

Attention Deficit Hyperactivity Disorder (ADHD) affects approximately 2.5% of adults and is characterized by persistent difficulties with attention, increased distractibility, and inattention errors. Despite a well-established clinical description, its neurobiological foundations remain incompletely understood, limiting the identification of robust biomarkers and the development of targeted therapeutic strategies.

In this context, an international study published on March 16 in the Journal of Neuroscience and conducted by researchers from Inserm (Institute of the Brain, Inserm/CNRS/Sorbonne University) and Monash University proposes an original pathophysiological hypothesis: ADHD symptoms could be linked to the intrusion of slow brain waves, typically associated with deep sleep, during wakefulness. This phenomenon, referred to as "local sleep," could serve as an explanatory mechanism for the attentional fluctuations and daytime sleepiness observed in these patients.

The authors compared brain activity in two groups of adults: 32 participants diagnosed with ADHD, under medication, and 31 neurotypical subjects. The recordings were made during the execution of a task requiring sustained attention, allowing for the simultaneous evaluation of behavioral performance and the associated neurophysiological dynamics.

The results revealed a significant increase in slow wave density among ADHD participants. "Adults with ADHD exhibit significantly higher slow wave density, typically observed during deep sleep. However, these waves are not insignificant: the higher their density, the more errors in attention participants make, and they exhibit slower or more variable reaction times," said Thomas Andrillon, Inserm researcher and the study's last author, in a press release.

Sleep intrusions correlated with fatigue

These slow-wave intrusions are also associated with specific subjective states, including an increase in episodes of "mind wandering" and "mind blanking." Furthermore, a positive correlation was observed between the accumulation of these waves and the level of fatigue experienced during the task.

The authors, however, emphasize that this phenomenon is not pathological in itself: "The intrusion of sleep waves is a perfectly normal phenomenon. Think of a long run: after a certain time, physical fatigue forces you to take a break. The same happens with mental fatigue: after a day of wakefulness or a poor night’s sleep, the brain also takes breaks in the form of slow waves. These brief moments of brain inactivity occur in everyone."

However, the increased frequency of these episodes in ADHD patients suggests an impairment of the wakefulness regulation mechanisms. The authors propose that these intrusions could be a central mechanism explaining performance fluctuations and difficulties in maintaining stable attention.

This research supports the hypothesis that ADHD could be, at least partially, conceptualized as a disorder of vigilance regulation. "These local sleep waves could become a key biomarker for diagnosis," Thomas Andrillon suggests.

Beyond diagnostic interest, these findings open therapeutic perspectives, particularly in the modulation of sleep and vigilance processes. Non-pharmacological approaches could be considered. "In neurotypical individuals, some studies, for example, have shown that auditory stimulation during sleep can enhance nocturnal slow waves, which could reduce the occurrence of brain activity resembling sleep during wakefulness the next day. A next step will be to determine whether this approach could also reduce these local sleep intrusions in people with ADHD," concludes the researcher.

The identification of these neurophysiological signatures paves the way for a better characterization of ADHD and the exploration of new intervention targets centered on the interactions between sleep and cognition.