Delta Waves and Cognitive Recovery During a Restricted Sleep Opportunity After Total Sleep

Exposure to sleep debt is one of the many stresses to which military personnel are exposed, during operational deployments or high-intensity training1.

The kinetics of cognitive performance degradation during acute sleep restriction or deprivation are relatively well studied in the literature2, with significant inter-individual variability. Restoring these cognitive functions requires sufficient sleep, sometimes for several days. However, the military work environment often offers only limited opportunities for recovery, which does not allow for ad integrum restoration of cognitive capacities, although some subjects recover better than others.

This is problematic in an environment where individual and collective performance levels are a prerequisite for safety and mission success3.

In this context, early identification of poor recuperators, who do not sufficiently restore their cognitive performance after periods of rest, would enable us to adapt more effectively the use of different countermeasures (sleep extension, naps, adapted use of caffeine...)4. This implies the availability of validated objective markers, as subjective assessments are often inadequate in this context. The temporal data classically derived from the analysis of sleep macrostructure (total sleep time, duration of wakefulness after falling asleep, time spent in the various sleep stages, etc.) are compromised when the opportunity for sleep is restricted. It therefore becomes pertinent to look for non-temporal markers that would testify to the efficiency of sleep's recuperative function.

Delta slow waves [1 - 4 Hz], which are mainly observed during deep slow-wave sleep on a sleep EEG, appear to be one of the indicators of the restorative function of sleep. They have been identified as a marker of sleep pressure5. The spectral power in this frequency range (delta power or slow-waves activity), obtained after fast Fourier transformation, bears witness to the activity of these waves. It is known to increase at the start of the night, particularly after sleep debt, and then gradually decrease, reflecting the dissipation of sleep pressure. It is recognized that high spectral power in this frequency range, particularly in deep slow wave sleep, is a marker of the "depth" of sleep" . This depth could guarantee the restorative function of sleep. [...]