0238 EFFECTS OF SIMULATED EARLY MORNING SHIFTWORK ON COGNITION

• Published in: Sleep (New York, N.Y.) Vol. 40; no. suppl_1; pp. A87 - A88
• Main Authors: Stothard, ER, McHill, AW, Ritchie, HK, Melanson, EL, Wright, KP
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 28.04.2017
• Subjects: Cognition & reasoning; Sleep; United States > US
• ISSN: 0161-8105; 1550-9109
• DOI: 10.1093/sleepj/zsx050.237

Abstract Introduction: Modern society requires 24h availability of goods and services, often provided by those working non-traditional hours; ~20% of the US workforce. Early morning shiftworkers are the largest population of shiftworkers in the US and relatively little research has examined the influence of such work hours on cognition. We therefore tested the impact of simulated early morning shiftwork on mathematical addition performance and subjective ratings of alertness, sleepiness and mood. Methods: 18 participants (9 female) aged 23.2 ± 3.8y (±SD) completed a 16-day protocol. Each subject completed two overnight in-laboratory visits in a randomized, counterbalanced order, separated by one week. Prior to each study visit, subjects maintained habitual, self-selected 8h sleep schedules for one week. One visit served as control where subjects were scheduled to sleep 8h at their habitual time. The other visit simulated an early morning shift where subjects were scheduled to sleep ~1h prior to habitual bed time and to wake up~2.5h prior to habitual wake time. After waking, cognition was initially tested for effects of sleep inertia and thereafter cognition was assessed every ~40 minutes for 4h. Results: Subjects attempted and correctly answered more two-digit number addition questions in the simulated early morning shiftwork condition compared to performance at habitual time during sleep inertia (0-2h awake) and after sleep inertia had dissipated (2-4h awake) (both p<0.05). In contrast, subjects reported increased ratings of subjective sleepiness on the Karolinska Sleepiness Scale and decreased ratings of alertness, clear-headedness, competence, motivation, sharpness, and quick-wittedness during the early morning shiftwork condition (all p<0.05). Conclusion: Contrary to our hypothesis, cognitive function was better during simulated early morning shiftwork versus that seen after awakening at habitual wake time, despite worse subjective ratings. Better performance in the early morning shift work condition could be related to the circadian timing of performance as, from a circadian perspective, forced desynchronony protocols indicate performance is worst near and shortly after habitual wake time. Support (If Any): University of Colorado Boulder Dean’s Graduate Student Research Grant; NIH DK092624 and TR001082.