Afternoon sleep in certain hypersomnolent states: “intermediate sleep”

Abstract

Spontaneous afternoon sleep was studied polygraphically and clinically in eleven patients with diverse types of diurnal hypersomnolence and in four controls (3 of whom were not recorded). All the tracings showed normal EEG sleep patterns. Sleep stages III and IV were rarely reached and rapid eye movement (REM) sleep only appeared in a cataplectic-narcoleptic and in a patient under light barbiturate sedation. All the tracings showed predominance of intermediate sleep, composed of light slow wave sleep and accompanied by slow or, especially, medium fast eye movements and the presence of twitches and jerks. The nature and importance of intermediate sleep and its relationship to slow wave sleep on the one hand and to REM sleep on the other is discussed. A hypothesis is proposed whereby there is a constant potential possibility for REM sleep to appear but this possibility, under normal conditions, is totally inhibited by wakefulness and slow wave sleep and only partly inhibited by light slow wave sleep.