0447 Differential Effects of CBT-I and Bright Light Therapy on Inhibitory Control and Risk-Taking Behavior in Youths with Comorbid Insomnia and Eveningness

Introduction Comorbid insomnia and eveningness are common in youth. Although cognitive behavioral therapy for insomnia (CBT-I) is well-established, it is unclear how CBT-I combined with circadian-targeted bright light therapy (BLT) impacts impulsivity-related cognitive processing in this population. This study examined effects of CBT-I with and without BLT on inhibitory control and risk-taking behavior using computerized neurocognitive tasks in youths with comorbid insomnia and eveningness. Methods A total of 146 participants (mean age = 19.9, SD = 3.2, 55.5% female) with DSM-5 insomnia disorder and eveningness (Reduced Morningness–Eveningness Questionnaire ≤ 11) were randomized into six weeks of CBT-I with BLT (CBT-I+BLT, N = 50), CBT-I with placebo light (CBT-I-BLT, N = 53), or waitlist group (N = 43). Inhibitory control and risk-taking behavior were assessed using Cue Go/No-Go (CGNG) task and Balloon Analogue Risk Task (BART). Linear mixed models were applied controlled for age, gender, depression and time of testing. Results In the CGNG task, significant Time×Group interactions were found for Cue and No-cue Reaction times (RTs) (Cue: F = 3.21, p = 0.044; No-cue: F = 3.50, p = 0.033), with only CBT-I-BLT group showing significant longer RTs from pre to post-treatment (cue: p = 0.001; No-cue: p = 0.003) without increased inhibition errors, suggesting enhanced response caution. In BART, a significant Time×Group interaction was observed for overall risky behavior attempts (All adjusted pumps: F = 3.25, p = 0.042). Both CBT-I+BLT (d = 0.59, p = 0.019) and CBT-I-BLT groups (d = 0.62, p = 0.025) had increased adjusted pumps relative to waitlist, suggesting heightened exploratory engagement. Notably, only CBT-I+BLT demonstrated a significant within-group increase in total earnings (d = 0.26; p = 0.046), suggesting adaptive risk-taking behavior. No other behavioral indices showed significant between-group differences. Conclusion CBT-I significantly enhanced response caution and adjunct BLT further improved adaptive risk-taking, reflecting changes in impulsivity-related cognitive processing in youths with insomnia and eveningness. Future studies could examine the mechanisms (e.g., reward processing) underlying these decision-making changes following CBT-I and bright light therapy. Support (if any) General Research Fund from the Hong Kong Research Grants Council awarded to SXL (Ref. 17608918).