Sequential amplitude variations in alpha band component in human electroencephalograms during sleep onset

The purpose of this research is to elucidate the amplitude variations of alpha band component in human electroencephalographic records during the transition between wakefulness and stage 1 sleep. The records from 16 adult male subjects were mathematically analyzed in successive 3-s epochs using a unique method of calculation (RLSSR). Amplitude variations are described herein. (i) General amplitudes are high during wakefulness and low during stage 1 sleep. Irregular fluctuations in amplitude are superimposed on these two levels. (ii) A large, steep, characteristic decline occurs during wakefulness. Two EEG patterns at the bottom of the decline represent arousal and EEG in stage 1 sleep, and these are referred to as big-decline-w and big-decline-s. The transition between the two levels appears as a big-decline-s rather than a gradual decrease. (iii) Thirteen records showed a multiple big-decline-s pattern before stage 1 sleep. The period from the first to the last big-decline-s is referred to as the “approach period” to sleep. Three subjects had no such approach and only one big-decline-s that appeared at the end of wakefulness. (iv) The bottom of the last big-decline-s of the three sites, occipital, central and frontal, appeared simultaneously in 6 subjects, 9 had a one-epoch gap, and 1 had two such gaps. The decline of the slope of the last big-decline-s showed high regression to an exponential curve. It is suggested that this characteristic pattern is the significant index of psychophysiological transition from wakefulness to sleep.