During adolescence, circadian phase delay yields later sleep timing and greater social jetlag (SJL), coinciding with heightened reward-circuit reactivity as subcortical systems mature before prefrontal control. Evidence linking sleep timing to reward-related neural activation in youth is limited. We examined whether sleep timing and SJL are associated with neural activation during reward processing in adolescents. In individuals with fMRI data, mid-sleep on free days (MSFsc) and SJL were derived from the Munich Chronotype Questionnaire (MCTQ; n = 5678) and Fitbit data (n = 2245) in adolescents (10-13 years) from the ABCD dataset. Reward processing was assessed using the fMRI Monetary Incentive Delay task, dissociating anticipation (reward/loss vs. neutral) and feedback (hit vs. miss). Linear mixed-effects models relate BOLD activation in a priori regions (amygdala, striatum, orbitofrontal cortex [OFC], insula, cingulate and frontal subregions) to sleep metrics. Later self-reported MSFsc was associated with greater activation during reward receipt in the left amygdala and right lateral OFC (β = 0.05-0.06, p < 0.05). The OFC association persisted after adjustment for sleep duration, while the amygdala effect was attenuated. Higher self-reported SJL also predicted increased left amygdala activation during reward receipt (β = 0.05, p < 0.05). Fitbit-derived MSFsc and SJL were not associated with reward-related activation after correction for multiple comparisons. Self-reported later sleep timing and greater SJL were linked to heightened affective and regulatory neural responses during reward-feedback. The divergence between self-reported and Fitbit-derived findings suggests that subjective and objective sleep timing measures may capture distinct aspects of sleep timing with relevance for neural reward outcomes. Sleep timing, beyond duration, represents a modifiable target for improving adolescent circadian health. fdr fdr
