Many human endeavors require high-level cognitive performance situations (e.g., health care, military operations, space flight) along the whole nycthemera (i.e. the 24-h cycle).
It has long been established that both acute total sleep deprivation (TSD) and chronic sleep restriction impair ability to maintain wakefulness, increase subjective sleepiness and sleep propensity, and most critically reduce various aspects of cognitive performance. In studies conducted in both laboratory setting and different professional situations inducing insufficient sleep, the most consistently and dramatically impacted cognitive capacities were sustained attention and alertness. This degradation of cognitive performance after a period of sleep deprivation is linked to an increase of sleep pressure, e.g. a reduction in the latency to sleep onset or increase of number of involuntary micro sleeps.
To identify countermeasures to deleterious effects of sleep deprivation is critical in many professional areas.
Management of wake/sleep cycle appears to have an important impact of alertness during sleep deprivation (e.g. sleep habits or physical activity, see the review. Recently, Rupp and coll. (2012) reported that one week of sleep extension realized before one week of sleep restriction (3 h/night) influence the rate of degradation of cognitive performance and alertness during this period and the subsequent recovery period. In other words, they proposed that sleep can be "banked" before a period of sleep loss and may help sustain performance and alertness. With a different experimental paradigm (i.e. without subsequent sleep deprivation), studies have shown that sleep extension (realized over different periods of time) may improve physical performance, attentional performance, or mood. The fact of increasing total sleep time over a period of time represents an attractive non-pharmacological countermeasure to limit the deleterious effects on performance induced by sleep privation. However, there is no study with cross-over and randomized design to assess effect on relatively short period (6 nights) of sleep extension on performance before, during total sleep deprivation and recovery. Moreover, there is no direct measurement of sleep pressure as continuous EEG monitoring to quantify micro sleep episode during period of sleep deprivation and effect of sleep extension on physical performance is not known.
Hence, the aim of this study was to assess the effects of 6 nights of sleep extension (EXT) on physical and cognitive performances, alertness and homeostatic sleep pressure before, during total sleep deprivation and the subsequent recovery day.
The investigators hypothesized that EXT would: i) partly prevents the physical and cognitive performances degradation-induced by total sleep deprivation ii) decreases the sleep pressure before, during and after total sleep deprivation and iii) improves the recovery speed of physical and cognitive performances.
