Study objectives: The hierarchical definition of arousals from sleep includes a range of physiologic responses including microarousals, delta and K-complex bursts, and variations in autonomic system. Whether patterns in slow-wave electroencephalographic activity and autonomic activation are primary forms of arousal response can be addressed by studying effects of total sleep deprivation. We therefore examined changes in arousal density during recovery sleep in healthy subjects.
Design: Participants spent 6 consecutive 24-hour periods in the laboratory. Nights 1 and 2 were baseline nights followed by 64-hour total sleep deprivation, then 2 consecutive recovery nights.
Setting: Sleep-deprivation protocol was conducted under laboratory conditions with continuous behavioral and electrophysiologic monitoring.
Participants: Twelve drug-free men aged 27.4 +/- 7.9 years were studied. None reported sleepiness or altered sleep-wake cycle, and none had neurologic, psychiatric or sleep disorders.
Measurements and results: Arousals were classified into 4 levels: microarousals, phases of transitory activation, and delta and K-complex bursts. Sleep deprivation induced changes in the density of considered arousals except phases of transitory activation, with a distinct pattern among the different types. The greatest change was found for microarousals, which showed a significant decrease in the first recovery night (P = .01), with return to baseline thereafter. A fall in K-complex and delta-burst density was noted in the first recovery night, not, however, reaching statistical significance. The phases of transitory activation rate were virtually unaffected throughout the experimental nights.
Conclusions: We conclude that homeostatic sleep processes exert an inhibitory effect on arousal response from sleep with a significant effect only on the microarousal density. Decreased delta and K-complex burst rates, though not significant, support the hypothesis that they may be activating processes, probably modulated by factors independent from those implicated in cortical arousal.