[Activation of the brain and consciousness]

At least 3 levels of consciousness were identified within the stage B of sleep. Against the background of the increase in the alpha-rhythm amplitude, we observed an enhancement of voluntary and involuntary associations and increase in the flow of thoughts. The stage of "thought wandering" was accompanied by a considerable decrease in the alpha-rhythm regularity, a decrease in its frequency, and decrease in EEG coherence in all brain areas under study. At the stage of the "flat" EEG, the subjects experienced inhibition of mental processes ("empty heady"), their consciousness as if "falling down" to the lowest Ego level. The subjects were aware of the transition from one stage to another and could fix the stages. Thus, the results showed that subjective changes of levels of consciousness corresponded to different stages of transition from wakefulness to sleep which was objectively determined by the EEG.