Sleep and neurobehavioral performance during a 14-day laboratory study of split sleep/wake schedules for space operations

This laboratory study of 90 healthy adults investigates human performance impairments resulting from sleep restriction in order to examine whether splitting sleep into a shortened nocturnal sleep period and a diurnal nap results in less impairment than a consolidated sleep period of the same total daily duration. This research is directly relevant to space operations in which high-level sustained neurobehavioral performance demands are coupled with constrained mission schedules as there is evidence that even modest sleep restriction results in impairments that reduce productivity and increase the risk of catastrophic accidents due to fatigue-related human error. Recent research has led to my hypothesis that split-sleep schedules with reduced total daily sleep time could result in increased total wake time while preventing cumulative reductions in waking cognitive function. To test this hypothesis, quantitative measurements of neurobehavioral performance were studied in a ground-based, laboratory experiment that included N=90 subjects, each assigned to one of 18 split-sleep regimens during 10 days of sleep restriction. The main result was that across a range of chronic nocturnal sleep restriction conditions, with and without diurnal naps, neurobehavioral performance was primarily a function of total time in bed (TIB) per 24h. A secondary result was that there are circadian-phase dependent, sleep-dose dependent interactions between circadian and long-term homeostatic processes that build across days of sleep restriction. These results provide direct evidence that reductions in total daily sleep cause an accumulation of impairment regardless of whether sleep is scheduled as a consolidated nocturnal sleep period or split into a nocturnal anchor sleep period and a diurnal nap. Further, these impairments manifest as a function of circadian phase and sleep-dose across days of sleep restriction. In conclusion, split-sleep schedules provide no additional recovery benefits compared to schedules that include consolidated sleep of same total daily duration. Split-sleep, however, is operationally feasible if used to enhance the flexibility of sleep/work schedules for space operations involving restricted nocturnal sleep due to mission-critical task scheduling. These results are not only important for space exploration but are generally applicable to any continuous industrial operation that involves sleep restriction, night operations, and shift work.