A comparison of sleep deprivation and narcolepsy in terms of complex cognitive performance and subjective sleepiness

OBJECTIVES: (i) To expose 'normal sleepers' to a 32-h sleep deprivation protocol and evaluate the impact of this deprivation on a complex performance task i.e. the paced auditory serial addition test (PASAT). (ii) To compare these sleep deprivation performance findings with historical data on the impact of sleepiness secondary to narcolepsy on PASAT performance measures. (iii) To investigate the recuperative effects of a brief nap period on both sleepiness and PASAT performance for the sleep-deprived subjects. (iv) To compare these post-nap effects with historical data relating to the impact of napping on both sleepiness and PASAT performance for subjects with narcolepsy. BACKGROUND: Previous research has demonstrated that sleepiness induced by sleep deprivation in normal sleepers may lead to cognitive impairment across a range of performance tasks. Sleepiness secondary to narcolepsy has also been noted to impair cognitive function especially for complex processing tasks. Direct comparison of the effects of sleepiness on performance between non-pathological and pathological sleepiness states is confounded, however, by methodological differences in research design especially in relation to levels of induced sleepiness and performance task selection. The purpose of the current study was to undertake a sleep deprivation study that achieved a methodological match with published data evaluating the impact of sleepiness on cognitive performance for subjects with narcolepsy. This methodological matching allowed for a more precise comparison of the impact of sleepiness on performance between non-pathological and pathological sleepiness groups. RESULTS: Normal sleepers required a 32-h deprivation protocol to develop a subjective level of sleepiness that equated with that identified by subjects with narcolepsy. This induced sleepiness in normal sleepers did not result in any significant decrement in complex performance, a finding that was in contrast to the performance decrement previously found in subjects with narcolepsy with equivalent subjective sleepiness ratings. A 20-min nap produced more improvement in both arousal and cognitive processing performance for the subjects with narcolepsy than for the current sleep-deprivation cohort. CONCLUSION: This study identified significant differences in the impact of sleepiness on complex performance between non-pathological sleep-deprived subjects and subjects with narcolepsy. This paper explores these differences in relation to the potential for both quantitative and qualitative differences that exist in the nature of sleepiness between non-pathological and pathological sleepiness states.