[Neurophysiological basis of insomnia: role of cyclic alternating patterns]

During non-REM (NREM) sleep it is possible to identify two complementary conditions of arousal stability and arousal instability. Unstable sleep, which can be detected in all stages, is expressed by the recurrence of arousal complexes (sequences of K-complexes, delta bursts, K-alpha, conventional arousals), which translate a brief (10-15 s) activation of the sleeping brain. These repetitive arousal complexes compose the cyclic alternating pattern (CAP). During stable NREM sleep, arousal complexes are rare or absent and the EEG lacks any cyclic pattern (non-CAP). CAP is a spontaneous feature of normal sleep as it is typically involved in stage changes and nocturnal motor activity. The physiological amount of CAP rate (ratio of CAP time to NREM sleep time) varies with age according to a U-shape curve. Within these ranges, sleep is perceived as continuous and restorative. Conversely, an excess of CAP rate fragments sleep and impairs its quality. Polysomnographic investigation reveals that untreated insomniac patients exhibit significantly higher values of CAP rate compared to healthy sleepers. Effective hypnotic treatment restores physiological amounts of CAP rate, with specific differences between the administered drugs. The sensitivity of CAP parameters to drug manipulation can provide circumscribed information on the hypnotic properties of active compounds.