Effects of sleep inertia on cognitive performance following different time course naps after 30 hours sleep deprivation in healthy men

Abstract

Objective To study the effects of sleep inertia (SI) of different time course sleeps on sleep stages and cognitions in healthy men after 30 h sleep deprivation, and also to investigate the mechanism of cognitive functions impairment in sleep inertia stages and the influential factors of sleep inertia. Methods Ten healthy men (age, (20.8±2.1) years) participated in the program. The program was divided into 2 stages. First，participants attended a series of tests after 20 min nap（20 min nap group）after 30 h sleep deprivation. The testing series included 3 parts: the continuous performance task，the Stroop Tests, and the Addition Tests. The series of tests were done 3 times immediately after the volunteers were awoken and each lasted about 15 minutes with an interval of 10 minutes between each test. The polysomnogram (PSG) was recorded during the nap. The following 7 days was set as washing-out period to ensure a complete recovery. Participants repeated the similar processes with 2 h nap（2 h nap group） instead of 20 min nap. The cognitive performance of each group was compared with each other along with the best cognitive performance in awakening to estimate whether or not the cognitive abilities regained the normal condition. Results (1) Sleep latency became shortened in both groups after 30 h sleep deprivation. There were no slow wave sleep (SWS) and rapid eye movement sleep (REM) sleep stages in the 20 min naps, while the percentage of SWS was increased and percentage of REM declined in 2 h naps.（2）In the early of SI (5 min after awaking), cognitive tasks showed that the abilities of continuous attention，selected attention and addition ability were all impaired（continuous performance task：（371.8±21.3） times/3 min vs （334.4±22.4) times/3 min，(373.2±19.0) times/3 min vs (323.7±23.8) times/3 min，t=10.443, 7.774，both P<0.01; Stroop tests:(20.3±1.5) points vs（17.3±1.0) points，（21.5±0.8）points vs（16.1±1.4）points，t=8.478,4.934，both P<0.05; Addition Tests:（222.2±13.2） s vs（266.6±23.7） s, (226.3±10.9) s vs（267.6±23.4）s，t=5.748,6.685，both P<0.01）.The cognitive functions impairments of 2 h nap group were more severe at the initiation of sleep inertia, but regained the normal condition more quickly. Different cognitive tasks recovered at different speeds. The dispersion of SI needed 30 min. Conclusions (1) There are difference in the sleep construction and awaked sleep stage between 20 min nap and 2 h nap groups. (2) SI exerts negative influences on cognitive performances of continuous attention，selected attention and addition after sleep deprivation. Many factors may influence the dispersion of SI, including sleep debt, compensation of sleep debt and others. (3) Fragments of sleep are unfavorable to the recovery of body. Key words: Sleep deprivation; Sleep disorders; circadian rhythm; Wakefulness; Cognition; Polysomnography