Precursors of the evoked K-complex in event-related brain potentials in stage 2 sleep

The aim of the study was to examine precursors of the evoked K-complex as manifested in event-related brain potentials (ERPs) during stage 2 sleep. ERPs to infrequent deviant tones of 1100 and 2000 Hz and immediately preceding frequent standard tones of 1000 Hz were compared between trials containing and trials not containing a K-complex (KC trials, NO KC trials, respectively) to the deviant tones. The N350 wave to the deviant tones was markedly larger during the KC than during the NO KC trials. Also the P210 wave to the 2000 Hz deviant tone showed the same phenomenon. No definite evidence was found for the mismatch negativity-like deflection during the KC trials. ERPs to the standard tones presented immediately (625 ms) prior to the deviant tones showed a larger early positive wave during the KC trials than during the NO KC trials. No corresponding phenomenon could be observed for the identical standard tone presented 1250 ms prior to the deviant tones. In all, the results suggest that the sleeping brain is momentarily more responsive to incoming sensory events preceding a K-complex than preceding a no K-complex response to a stimulus.