The key role of daytime sleepiness in cognitive functioning of adults with attention deficit hyperactivity disorder

Helfer, Bartosz; Bozhilova, Natali; Cooper, Ruth E.; Douzenis, Joanna I.; Maltezos, Stefanos; Asherson, Philip · 2020 · Crossref

DOI: 10.1192/j.eurpsy.2020.28

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Summary

This study investigates the extent to which daytime sleepiness contributes to cognitive deficits in adults with attention deficit hyperactivity disorder (ADHD), challenging the view that these deficits are solely intrinsic to the disorder. While sleep disorders are common comorbidities in ADHD, the specific role of on-task sleepiness in driving cognitive performance issues remains underexplored. The authors hypothesized that adults with ADHD would exhibit higher levels of sleepiness than neurotypical controls and that this sleepiness, rather than ADHD symptom severity alone, would significantly impair cognitive functioning. The researchers analyzed data from 111 adults (81 with ADHD, 30 controls) recruited from the OCEAN clinical trial. Cognitive performance was assessed using the Sustained Attention Response Task (SART) and the Cued Continuous Performance Task with flankers (CPT-OX), measuring omission errors, commission errors, and reaction time variability. On-task sleepiness was evaluated using an observer-rated protocol based on video recordings during the SART. Additionally, electroencephalogram (EEG) slowing, calculated as the ratio of slow (delta/theta) to fast (alpha/beta) frequency bands, was measured during a resting state to assess physiological arousal. ADHD symptom severity was measured via the Conners’ Adult ADHD Rating Scales, and sleep quality via the Pittsburgh Sleep Quality Index. Results indicated that adults with ADHD were significantly sleepier than controls during the cognitive task, with sleepiness increasing over time. EEG slowing was also significantly higher in the ADHD group, particularly in frontal regions, where frontal delta activity was nearly double that of controls. Crucially, when a subgroup of "sleepy" participants was identified, they exhibited the highest rates of omission errors and reaction time variability, exceeding even the non-sleepy ADHD group. Statistical analysis revealed that observer-rated sleepiness strongly predicted omission errors in the SART, independent of ADHD symptom severity and IQ. In contrast, ADHD symptom severity did not significantly predict these errors when sleepiness was accounted for. EEG slowing correlated with both ADHD diagnostic status and symptom severity. The findings suggest that cognitive performance deficits often attributed to ADHD, such as increased omission errors and reaction time variability, are largely driven by on-task sleepiness rather than core ADHD symptoms. The elevated frontal EEG slowing and delta activity may reflect underlying hypo-arousal or residual effects of early developmental hypoxic events. The study concludes that daytime sleepiness plays a major role in the cognitive functioning of adults with ADHD, implying that clinical assessments and treatments should prioritize sleep management to improve cognitive outcomes. The authors also validate an observer-rated sleepiness protocol as a useful tool for future research in psychiatry and psychology.

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• drowsiness