Late component variants of single auditory evoked responses during NREM sleep stage 2 in man

The morphological variance of single EEG responses evoked by invariable auditory stimuli during SWS stage 2 was analysed in 2 nights of 6 healthy young adults. The latency and the peak-to-peak amplitude of the maxima and the consecutive minima of the EEG epochs following the stimuli were measured. Pointing out general characteristics of the responses, highly variable during SWS, amplitude and latency histograms of the maxima and minima were used and particular morphological patterns were differentiated. The percentages of these patterns for the nights studied were calculated. The modus of the amplitude histogram of the group examined is the class of amplitudes between 41 and 80 microV. Approximately 40% of the single responses are identical with the visually detectable K complex. The distribution of amplitudes proved to be unimodal. The continuous transition between the visually undetectable and the extremely high voltage responses indicates that K complexes are variants of evoked potentials. Higher probability of occurrence is found in two latency ranges for both the maxima and minima. The peaks of the latency histograms of these points could be identified with the latencies of the Weitzman's N2, N2b, P3 and the P3a (labelled by us) components of the averaged AEP. The possible connection between the variety of the late components of EPs in SWS and information processing connected to arousal-orientation mechanisms in sleep is discussed.