Sleep Architecture Abnormalities, Cognitive Performance Deficits, and CBT-I Efficacy in Adults with Chronic Insomnia Disorder

Chronic insomnia disorder, defined by persistent difficulty initiating or maintaining sleep with associated daytime impairment occurring at least three nights per week for three or more months, is the most prevalent sleep disorder in Europe, affecting an estimated 10–15 percent of adults and generating substantial individual burden through impaired cognitive performance, emotional dysregulation, and elevated risk of depression, anxiety, and cardiovascular disease. Despite evidence-based cognitive behavioural therapy for insomnia (CBT-I) representing the recommended first-line treatment over pharmacotherapy in all major clinical guidelines, access to trained CBT-I therapists remains severely limited across European healthcare systems. This randomised controlled trial compared six-week group CBT-I with a sleep hygiene education control in 400 adults with polysomnography-confirmed chronic insomnia disorder, evaluating the effects on sleep architecture (PSG), EEG spectral power, Insomnia Severity Index, actigraphy parameters, and next-day cognitive performance over a twenty-four-week follow-up. CBT-I produced significant improvements across all primary outcomes. Insomnia Severity Index score declined from 18.4 to 5.2 at week twenty-four (remission rate 68.4%) compared to 18.2 to 16.0 in the sleep hygiene control (remission rate 12.8%). PSG-measured sleep efficiency improved from 68.4 to 84.2 percent in the CBT-I arm, with significant reductions in wake after sleep onset (WASO: from 82.4 to 34.8 minutes) and sleep onset latency. EEG spectral analysis revealed significantly higher delta power and lower beta power during NREM sleep in CBT-I responders at follow-up, consistent with restoration of slow-wave sleep drive and reduction of cortical hyperarousal. Next-day cognitive performance improved significantly in the attention, working memory, and executive function domains.