Study on occurrence of microsleep during psychomotor performance and criteria for its detection

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Background : Microsleep is usually described as a sudden, short-lasting burst of stage 1 sleep or ultrashort phase of sleep. With all clinical observations, such as automatic syndrome in hypersomniacs, and mood and psychomotor performance in depressed patients, few basic researches have been made and it seems to remain open whether microsleep should be considered as sleep or not.Method : The main aim of this study was to examine the behavioral and physiological features of microsleep during maintenance of wakefulness by psychomotor performance, and to explore the criteria for detection of microsleep. Electroencephalograms(EEGs), electrooculograms(EOGs) and finger tappings were continuously recorded over 40 min in the afternoon in 15 subjects. Subjects were instructed to perform 10-successive tappings with a subjectively estimated interval of 1 sec and a force of about 1 Kg. Ten-successive tappings were supposed to perform alternately on each of right and left hands (Dual Alternation Ta … More sk of Finger Tapping). Awakening tone was presented after no movement of tapping had lasted 70 sec. EEG power spectra were estimated by using maximum entropy method. The method, based on the application of a moving linear regression analysis, was applied to automatic detection and measurement of slow eye movements and tappings. Tap-by-tap analyses were made on EEG,EOG and tapping data.Results : A specific state to microsleep was present, behaviorally characterized as the repeated occurrence of mistakes, including lowered force, delayed interval and lapse, and corrections of finger tappings. Duration of microsleep was found to range from 2 to 7 sec on the basis of analysis of inter tap interval and alternation gaps between hands. Physiologically significant changes were seen during a few seconds before lowered-force tappings : disappearance of dominant frequency of alpha band, decreased EEG power ratios of alpha/theta and alpha/beta bands, and appearance of slow eye movements. These changes occurred even in normal train of tapping as well as in interrupted one.Conclusion : The following features might be help with detection of microsleep : 1)Finger tapping with force decreased by half, 2)Alpha /theta power ratio with a value of 1 (central EEG) and a value of 4 (occipital EEG), 3)One or more appearance of slow eye movements. Less