O021 Distinguishing Circadian from Sleep Effects on Cognitive Performance During a Simulated Night Work Lighting Intervention

Abstract Introduction We previously found that a circadian-informed lighting intervention accelerated circadian retiming, improved cognitive performance and sleep during 4-days of simulated nightwork. This study explores the independent and combined effects of circadian retiming and sleep duration on cognitive performance improvements with circadian-informed lighting. Methods Data were from 19 healthy sleepers (12 male; mean±SD aged 29 ±10 y) underwent two 8-day in-lab protocols with circadian and control lighting. On days 3-7, participants transitioned to day sleeps (10:00–19:00) and underwent cognitive tests simulating nightwork (00:00–08:00). Cognitive performance was measured by psychomotor vigilance task (PVT) lapses. Polysomnography measured total sleep time (TST) during each sleep. Core body temperature minimum (Tmin) was estimated via ingestible capsules. Multilevel generalized structural equation modelling tested the mediation effect of TST on the relationship between Tmin and PVT lapses, and the moderating effect of lighting intervention on all three pathways. Results For both mediating pathways between Tmin and TST, TST and PVT are not moderated by lighting intervention (B = 16.81, SE = 8.99, p =.062 and B = 0.00, SE = 0.97, p =.332 respectively) so we can conclude there is no moderated mediation effect. There was a moderated direct effect of lighting intervention on Tmin time and worse PVT time (B = -0.64, SE = -3.74, p<.001). Discussion While homeostatic and circadian processes impact sleep and cognitive performance, PVT performance improvements from circadian-informed lighting appear to be dominated by circadian retiming effects rather than longer sleep under night shift work conditions.