Increased production of evoked and spontaneous K-complexes following a night of fragmented sleep.

STUDY OBJECTIVES To determine whether K-complex production is better interpreted as being an arousal response or reflective of a sleep protective micro-state. DESIGN A 3-night study--night 1 as a baseline night, night 2 as a sleep fragmentation night, followed immediately by night 3 as a recovery night. On nights 1 and 3, approximately 400 auditory stimuli were presented during nonREM sleep in the first two sleep cycles, using stimulus parameters previously found to be optimal for K-complex production. SETTING The sleep research laboratory at the University of Melbourne. PARTICIPANTS Six young healthy subjects (3 female). INTERVENTIONS One night of sleep fragmentation. Ten-second auditory tones of up to 110 dB were presented throughout the entire night at approximately 1-minute intervals. MEASUREMENTS AND RESULTS Sleep drive was increased on the recovery night, as indicated by increased amounts of slow wave sleep, increased sleep efficiency, and a reduction in stimulus-related alpha activity. The incidence of both evoked and spontaneous K-complexes increased significantly on the recovery night. When K-complex trials were averaged, neither N550 (Fz) amplitude nor latency differed between the 2 nights. When vertex sharp waves were averaged, N350 (Cz) amplitude was increased significantly on the recovery night. CONCLUSIONS The increase in K-complex frequency together with the decrease seen in stimulus-related alpha activity supports the view that they reflect a sleep maintenance, rather than an arousal, response.