The purpose of this study isto investigate the effect of dawn simulated light and sleep stages just before awakening on subjective feelings of awakening. A counterbalanced study was performed on different one night, totally two nights, one of which was control day (no dawn simulation), and another one was experimental (dawn simulation). Twenty healthy participants took part in a laboratory protocol. PSG was recorded during nocturnal sleep. The amount of light before awakening was estimated by the sleeping position per second. Subjective sleepiness evaluated using OSA sleep inventory is significantly reduced in the dawn condition as compared with control condition for participants awaken from NREM sleep (p < 0.05). In participants awaken from NREM sleep with appropriate amount of light exposure before awakening, sleepiness also shows a significant decrease (p < 0.01) as compared with control condition. However in participants awaken from phasic REM sleep, there is no significant difference in sleepiness between two conditions. In participants awaken from NREM sleep, sleepiness is significantly correlated with the amount of light exposure before awakening (r=0.56, p < 0.05). These results suggest that for the better awakening, not only appropriate amount of light exposure before awakening but also a sleep state just before awakening should be considered.

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To assess the diversity of eye movements during sleep, this study automatically measured eye movements during hypnagogic state and REM sleep by applying a moving liner regression analysis to 22-overnight electrooculographic recordings which were based on the standard polysomnography. Analyses of feature-extracted parameters revealed that the traditional dichotomy of REMs and SEMs seemed to be unsatisfying and need to add the intermediate type of eye movements (IEMs) that partially had physical properties of REMs and SEM; IEMs were composed of two types of subtypes of gross eye movements (GEMs) and SEMs with sharp rising. These various eye movements were common to but depended on hypnagogic state and REM sleep. During hypnagogic state, where SEMs were more predominant, both SEMs and REMs declined as a function of time. In REM sleep, REMs showed one or two periods of bursts, and SEMs continuously appeared with or without bursts of REMs. The results may evidence that the diversity of eye movements occurs commonly in hypnagogic state and REM sleep and its appearance differs, depending on sleep state. Neuronal mechanisms for generating eye movements during sleep and the relationship between eye movements and visual images in dreaming were discussed.

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