Human slow auditory evoked potentials during natural and drug-induced sleep.

The alterations of human slow auditory evoked potential (SAEP) were studied during the sleep-waking cycle. Simultaneous recording of the mean square and standard error curves proved helpful in obtaining more information on the EEG samples used for averaging. In both natural and drug-induced sleep the earlier SAEP components decreased or disappeared, while the later components increased. A significant lengthening of all SAEP peak latencies was found in all sleep stages during tone-burst stimulation. With click stimulation the peak latencies of most SAEP components remained constant. Due to the variability of individual SAEPs, the interpretation of averaged SAEPs was commonly more difficult in sleep as compared with wakefulness. The alterations of SAEPs during sleep are considered from the point of view of their exrralemniscal origin. The hypothesis is put forward that the activating (desynchronizing) and depressing (synchronizing) systems participate in the generation of the earlier and later SAEP components, respectively.