Awareness During Drowsiness: Dynamics and Electrophysiological Correlates

During drowsy periods, performance on tasks requiring continuous attention becomes intermittent. Previously, we have reported that during drowsy periods of intermittent performance, 7 of 10 participants performing an auditory detection task exhibited episodes of non-responding lasting about 18 s ( Makeig & Jung, 1996 ). Further, the time patterns of these episodes were repeated precisely in subsequent sessions. The 18-s cycles were accompanied by counterbalanced power changes within two frequency bands in the vertex EEG (near 4 Hz and circa 40 Hz). In the present experiment, performance patterns and concurrent EEG spectra were examined in four participants performing a continuous visuomotor compensatory tracking task in 15-20 minute bouts during a 42-hour sleep deprivation study. During periods of good performance, participants made compensatory trackball movements about twice per second, attempting to keep a target disk near a central ring. Autocorrelations of time series representing the distance of the target disk from the ring centre showed that during periods of poor performance marked near-18-s cycles in performance again appeared. There were phases of poor or absent performance accompanied by an increase in EEG power that was largest at 3-4 Hz. These studies show that in drowsy humans, opening and closing of the gates of behavioural awareness is marked not by the appearance of (12-14 Hz) sleep spindles, but by prominent EEG amplitude changes in the low theta band. Further, both EEG and behavioural changes during drowsiness often exhibit stereotyped 18-s cycles. Au cours des périodes de somnolence, la réussite de tâches faisant appel à une attention soutenue devient intermittente. Nous avons établi précédemment, que durant des périodes de somnolence avec réussite intermittente, sept des dix participants effectuant une tâche de détection auditive affichaient des épisodes de non-réponse qui duraient environ 18 secondes ( Makeig & Jung, 1996 ). Par surcroît, les structures temporelles de ces épisodes ont été répétées de façon précise au cours de séances subséquentes. Les cycles de 18 secondes s'accompagnaient de changements d'intensité équilibrés à l'intérieur de deux bandes de fréquence du vertex de l' EEG (près de 4 Hz et vers 40 Hz). Dans la présente expérience, les patrons de performance et les spectres d' EEG concomitants ont été examinés chez quatre participants exécutant une tâche visuomotrice de poursuite compensatrice continue, en rondes de 15