Is the appearance of mismatch negativity during stage 2 sleep related to the elicitation of K-complex?

There is no convincing evidence for the occurrence of mismatch negativity (MMN) elicited by infrequent deviant tones in a homogenous tone stream during sleep in adult humans. Also the data presented here failed to show an MMN during any stage of sleep when event-related potentials (ERPs) were averaged across all trials of the same sleep stage. The aim of the study was to determine whether the MMN appearance during sleep is related to the variations in microstates of sleep that differ in terms of stimulus elicited phasic EEG events. The focus was on stage 2 sleep. The single responses to a deviant tone were classified into 3 types during stage 2 prior to averaging ERPs. These 3 response types included K-complex, other phasic EEG events and no visually discernible phasic EEG events. The results showed that an MMN-like deflection indeed appeared during stage 2 but only when the deviant tone also elicited a K-complex. This type of deflection was not seen when the deviant tone was presented without the intervening standard tones. This supports the hypothesis that a true MMN to the deviant tone was seen during stage 2 sleep preceding a K-complex.