K‐complexes: are they signs of arousal or sleep protective?

Abstract

SUMMARY  The number of K‐complexes recorded at the central‐temporal EEG derivation (C3‐T3) during 5 min periods for both the ascending and descending phase of Stage 2 of NREM sleep for cycles 1,2… etc. were counted in 10 subjects for each of the following five groups: normal persons, patients with a primary generalized form of epilepsy, narcolepsy, insomnia and obstructive sleep apnoea. The differences in time spent in different stages of sleep were as expected for these types of patients. A 2‐within, 1‐between factors, repeated measure ANOVA was applied to the data on K‐complexes. Overall, there was no significant difference between the number of K‐complexes observed during the ascending and descending phases of the different sleep cycles. Patients with a sleep disorder had significantly less well‐defined K‐complexes than the normals and the patients with a primary form of generalized epilepsy: for insomnia (P= 0.035), for apnoea (P= 0.011) and for narcolepsy (P= 0.001). There was a significant, but very low correlation coefficient between the number of K‐complexes observed during Stage 2 of NREM sleep and the time spent during that stage for all groups combined (Rho 0.27, P= 0.002) and for the narcoleptic patients (Rho 0.44, P= 0.017). In all, the findings lend support to the hypothesis that a K‐complex can be seen as a ‘defensive response’, or has a sleep protective function. © 1995 European Sleep Research Society