Physiological Sleep Tendency and Ability to Maintain Alertness at Night

The maintenance of wakefulness test (MWT) and repeated test of sustained wakefulness (RTSW) were compared to the multiple sleep latency test (MSLT) during nighttime hours to evaluate differential sensitivity to variation in physiologic sleepiness/alertness. The degree of sleepiness varied by time of night and was further manipulated by varying prior sleep. Seven healthy normal sleepers were evaluated on the MWT, RTSW, MSLT, a digit symbol substitution test and the Wilkinson addition test in a protocol beginning at 2200 h and terminating at 0830 the following morning. A counterbalanced, crossover design compared an evening nap condition to a no-nap condition. The MWT and RTSW discriminated between nap and no-nap conditions, but the MSLT did not. This suggests that in some situations the MWT and RTSW may be more sensitive to changes in physiologic sleepiness/alertness than the MSLT. The data are discussed in terms of possible methodologic limits of the MSLT and the relationship between physiologic sleep tendency and the capacity to maintain alertness.