The role of the spontaneous and evoked k-complex in good-sleeper controls and in individuals with insomnia.

STUDY OBJECTIVES: Spontaneous and evoked K-complexes are believed to reflect a mechanism of sleep protection, yet their functional role remains a subject of debate. Studying the K-complex in primary insomnia, for which sleep protection appears to be of central importance, may provide further insight on its role. The purpose of the present study was to determine the role of spontaneous and evoked K-complexes in good sleepers and to investigate its role in primary insomnia. PARTICIPANTS: Twelve individuals with primary insomnia (mean age = 45.4 years) and 12 good-sleeper controls (mean age = 44.3 years). METHODS AND PROCEDURE: Participants underwent 4 consecutive nights of polysomnographic recordings. Spontaneous K-complexes (SKC) were analyzed during continuous stage 2 sleep on the third night, whereas evoked K-complexes (EKC) were elicited by auditory stimuli on the fourth night. Relative spectral power was measured on 1-second electroencephalographic segments prior to and following SKC, EKC, and trials in which auditory stimuli did not elicit a K-complex (EKC-). K-complex amplitudes were also measured. RESULTS: Measures of relative spectral power showed significant changes following EKC (increase in activity in the delta frequency band and decrease in activity in the theta, sigma, beta, and gamma frequency bands) and SKC (increase in activity in delta frequency band and decrease in activity in theta, alpha, sigma, and beta frequency bands) for good sleepers, whereas there was no such marked change in electroencephalographic activity surrounding EKC-. A similar pattern of electroencephalographic activity was also observed for the insomnia group on trials of each different K-complex. Auditory stimuli elicited the same proportion of EKC for both groups, whereas SKC density was higher for the insomnia group (1.52 SKC/min) than for good sleepers (1.06 SKC/minute) CONCLUSION: These results suggest that the SKC and the EKC both promote deeper sleep, further supporting a sleep-protection role.

Spontaneous K-complexes in chronic psychophysiological insomnia.

OBJECTIVE: Spontaneous K-complexes are electroencephalographic features unique to non-rapid eye movement sleep. It has been suggested that this phasic event is a sleep-protective mechanism. Because insomnia sufferers report poor sleep quantity and quality, the objective of this study was to document the occurrence of spontaneous K-complexes in Stage 2 sleep of individuals with chronic insomnia. Specifically, the number and density of spontaneous K-complexes were studied in psychophysiological insomnia sufferers. SETTING: This study took place in a sleep and event-related potentials laboratory. DESIGN: Spontaneous K-complexes were scored during Stage 2 sleep on the second and third nights of a four-consecutive-nights protocol of polysomnographic recordings. PARTICIPANTS: The sample included 14 participants suffering from psychophysiological insomnia (INS group; mean age=44.1 years) and 14 good sleepers (mean age=38.1 years). Participants underwent sleep and psychological evaluations. INS group participants met the diagnostic criteria for primary psychophysiological insomnia (mean duration of insomnia=9.6 years). INTERVENTION: Not applicable. RESULTS: The total number of spontaneous K-complexes and the density according to the total time spent in Stage 2 sleep (spontaneous K-complexes per minute) were compiled. Repeated-measures analyses of variance showed no significant difference in the number and density of spontaneous K-complexes between the INS group (313.98 and 2.66) and the GS group (361.10 and 2.88), respectively. CONCLUSION: These results suggest no deficiency in the sleep-protective mechanism of psychophysiological insomnia sufferers in comparison with good sleepers, as measured by the spontaneous K-complexes' number and density.