EYELID MOVEMENTS AND MENTAL ACTIVITY AT SLEEP ONSET

The nature and time course of sleep onset (hypnagogic) mentation was s tudied in the home environment using the Nightcap, a reliable, cost-ef fective. and relatively noninvasive sleep monitor. The Nightcap, linke d to a personal computer, reliably identified sleep onset according to changes in perceived sleepiness and the appearance of hypnagogic drea m features. Awakenings were performed by the computer after 15 s to 5 min of sleep as defined by eyelid quiescence. Awakenings from longer p eriods of sleep were associated with (1) an increase in reported sleep iness, (2) a decrease in the length of mentation reports, (3) a decrea se in the frequency of reports of normal, wake-like thoughts, (1) an i ncrease in the frequency of ''unusual thoughts,'' and (5) increased fr equencies of formal dream features, including visual hallucination, se lf representation, fictive movement, narrative plot, and bizarreness. While sleep-onset reports can include all features cf rapid eye moveme nt (REM) dream reports, the number of such features is markedly reduce d at sleep onset, suggesting that this mentation is a greatly diminish ed version of REM dreaming. (C) 1998 Academic Press.