0196 Late and Irregular Sleep-Wake Schedules Increase Sleep Propensity and Impair Neurobehavioral Performance, but Not Subjective Sleepiness in the Morning

Abstract Introduction While irregular sleep schedules are associated with poorer academic performance, delayed circadian timing, and adverse health, causal evidence remains limited. We conducted a randomized trial to probe the effects of sleep regularity on morning sleep propensity, neurobehavioral performance, and subjective sleepiness. Methods Healthy adults (n=25, 9F, mean±SD age: 27.2±3.8 years) completed a 26-day inpatient protocol that included an initial 24-hour baseline day, followed by 21 days on a randomized Early Regular (ER), Late Regular (LR), or Irregular (IR) sleep-wake/dark-light schedule, a subsequent 30-hour interval of 90-minute “ultradian days”, and a final 24-hour recovery day. Each randomized sleep-wake/dark-light schedule was based on observed schedules from a study in college students. Schedules were selected for regularity based on the Sleep Regularity Index being >80 for ER and LR schedules or < 60 for the IR schedule, and for timing as either Early (ER: scheduled sleep midpoint 3:57±0:39 h) or Late (LR: 6:29±0:40; IR: 7:01±1:58). Morning sleep propensity, the primary outcome, was measured using polysomnography-assessed sleep onset latency (SOL) averaged across sleep episodes scheduled at 7:30, 9:00, and 10:30. At 08:30 and 11:30, neurobehavioral performance was measured by a 10-minute PVT, with attentional failures (reaction time >500 ms) as the primary endpoint, and subjective sleepiness was assessed using a visual analogue scale. Results Schedule significantly impacted sleep propensity and attentional failures (both, p< 0.03) but not sleepiness (p=0.50). Compared to the ER schedule, which was associated with, on average, the longest SOL (29.32±4.76 minutes), SOL was significantly shorter in IR schedules (11.22±1.66 minutes, p< 0.01) but not in LR schedules (18.74±4.25 minutes, p=0.11). There were significantly fewer attentional failures in the ER compared to the LR (p< 0.01) and IR schedules (p< 0.03). Conclusion An early regular schedule is associated with lower sleep propensity and better neurobehavioral performance in the morning compared to late and irregular schedules. Increased morning sleep propensity and neurobehavioral performance impairment associated with late and irregular schedules was not recognized, since concomitant self-reported sleepiness scores did not differ among schedules; this has implications for behavior changes, learning, and safety. Support (if any) NIH R01-HL128538 & UL1 RR025758