O003 Investigating the relationship between core body temperature and changes in cognitive performance during simulated night shifts

INTRODUCTION: The timing of circadian and sleep-wake behaviours is disrupted by night shift-work. Interventions involving light may prove beneficial in adjusting the circadian rhythm to shift work, although the changes in vigilance remain uncertain. This study examined the temporal relationship between core body temperature (CBT) rhythm and vigilance during a work-shift through lighting. METHODS: 19 healthy individuals (12 males, mean±SD age of 28.7±10.4 years) participated in two 8-day experimental conditions with 4 days of circadian-informed lighting vs standard lighting. On Day 2, participants transitioned from a typical day-night wake-sleep schedule to night shift-work from 00:00 to 08:00 on Days 3 to 7. Psychomotor vigilance tasks (PVTs) were administered six times on shift. CBT was monitored via ingestible capsules. Daily CBT minimum (CBTmin) time was compared to the timing of the worst PVT performance on-shift (task with most lapses). RESULTS: In the parent study, circadian lighting improved on-shift performance and sleep quality. These effects were accompanied by a significant day-by-condition interaction effect on the degree of temporal offset between CBTmin time and worst PVT performance time during the work shift, F(3,74.660)= 4.09, p=0.01; the disparity increased over successive days under the influence of circadian-informed lighting compared to standard lighting., p<0.01. CONCLUSIONS: The modest adjustment in the timing of the worst on-shift performance provides support that circadian lighting improves on-shift performance. These results emphasise the importance of considering the combined impact of circadian rhythms, sleep patterns, and time-on-task effects on performance outcomes when assessing fatigue and implementing countermeasures to phase-shift biological rhythms.