Cognitive performance in adolescents with Delayed Sleep-Wake Phase Disorder: treatment effects and a comparison with good sleepers

The present study aimed to investigate whether Australian adolescents with Delayed Sleep-Wake Phase Disorder have impaired cognitive performance and whether chronobiological treatment for Delayed Sleep-Wake Phase Disorder improves adolescents' sleep, daytime functioning and cognitive performance. Adolescents with Delayed Sleep-Wake Phase Disorder (mean = 15.68 ± 2.1 y, 62% f) reported significantly later sleep timing (d = 1.03–1.45), less total sleep time (d = 0.82) and greater daytime sleepiness (d = 2.66), fatigue (d = 0.63) and impairment (d = 2.41), compared to good sleeping adolescents (mean = 15.9 ± 2.4 y, 75% f). However, there were no significant between-group differences (all p > 0.05) in performance on the Operation Span (ηp² = 0.043), Digit Span (forwards: ηp ² = 0.002, backwards: ηp² = 0.003), Letter Number Sequencing (ηp² < 0.001) (working memory) and Digit-Symbol Substitution Tasks (ηp² = 0.010) (processing speed). Adolescents with Delayed Sleep-Wake Phase Disorder went on to receive 3 weeks of light therapy. At 3 months post-treatment, adolescents with Delayed Sleep-Wake Phase Disorder reported significantly advanced sleep timing (d = 0.56–0.65), greater total sleep time (d = 0.52) and improved daytime sleepiness (d = 1.33), fatigue (d = 0.84) and impairment (d = 0.78). Performance on the Operation Span (d = 0.46), Letter Number Sequencing (d = 0.45) and Digit-Symbol Substitution tasks (d = 0.57) also significantly improved.