Introduction the Neurobiological Basis of Sleep Inertia,1 Which Refers to the Cognitive Performance Impairment, Grogginess and Tendency to Return to Sleep Immediately after Awakening2

THE NEUROBIOLOGICAL BASIS OF SLEEP INERTIA,1 WHICH REFERS TO THE COGNITIVE PERFORMANCE IMPAIRMENT, GROGGINESS AND TENDENCY TO RETURN TO SLEEP IMMEDIATELY AFTER AWAKENING2 IS UNKNOWN. Documented cognitive deficits due to sleep inertia include simple and complex reaction time, complex simulation, letter cancellation, logical reasoning, mental arithmetic, vigilance, and memory—in addition to confusion and disorientation—as reviewed by Dinges in 1990.3 Sleep inertia appears to be worse under sleep-loss conditions4,5,6 and to vary in magnitude and duration with circadian phase.4,7 Evidence suggests that sleep inertia may be associated with the sleep stage at the end of sleep8,9 as well as the overall depth of sleep and the intensity of non-REM sleep.4,10,11,12 Sleep inertia is particularly problematic and potentially dangerous in operational settings13,14 in which a high level of performance is required during the one to two hours after awakening.15,16 Countermeasures could provide insight into the mechanisms underlying sleep inertia. The present study is the first to employ a pharmacological approach to this end: sustained lowdose caffeine administration. Specifically, we investigated the effects of caffeine on sleep inertia under sleep-loss conditions.