ELSEVIER Electroencephalographyand clinical Neurophysiology 95 (1995) 414-425 Dynamics of slow wave activity in narcoleptic patients under bed rest conditions L. Nobili a,*, A. Besset b, F. Ferrillo a, G. Rosadini a, G. Schiavi a, M. Billiard b a Center for Sleep Medicine, Department of Motor Sciences, Center for Cerebral Neurophysiology, National Council of Research, University of Genoa, Genoa, Italy b Sleep and Wake Disorders Unit, Gui-de-Chauliac Hospital, Montpellier, France Accepted for publication: 6 June 1995 Abstract Following a baseline night recording, 9 narcoleptic subjects and 9 sex- and age-matched control subjects were maintained on 16 h of diurnal sleep deprivation. Thereafter subjects were submitted to a 32 h bed rest protocol in a sound- and light-attenuated room. The EEG was recorded and processed by a Fast Fourier Transform. Narcoleptics did not differ from controls in total sleep time over the whole 32 h, but spent more time sleeping during the daytime (DT). In both groups slow wave activity (SWA) showed an exponential decaying trend during the first night (NI); a similar exponential trend during the second night (N2) was evident only in controls. In controls SWA showed a circadian-circasemidian distribution that was hardly detectable in narcoleptics. Narcoleptics showed an ultradian distribution of SWA with periodic emergence every 4 h during DT and N2. Our data confirm that a homeostatic mechanism is evident in narcoleptics when stimulated by diurnal sleep deprivation, while circadian and circasemidian mechanisms are less evident during DT and N2. These findings suggest a different coupling between homeostatic sleep regulating processes and circadian drives to sleep in narcoleptics. Ultradian drives to sleep seem to be predominant in these patients, thus probably acting as a means for the avoidance of stressful attempts to counteract a weaker waking state maintenance mechanism. Keywords: Narcolepsy; Slow wave activity; Bed rest; Homeostasis; Circadian rhythm; Ultradian rhythm I. Introduction The pathophysiological mechanism responsible for ex- cessive daytime sleepiness and irresistible daytime sleep episodes in narcolepsy is still controversial. Nocturnal sleep of narcoleptic patients is often fragmented by an increased number of awakenings, as well as being charac- terized by low sleep efficiency and low levels of slow wave sleep (SWS) (Rechtschaffen et al., 1963; Mont- plaisir, 1976; Montplaisir et al., 1978). Laboratory (Rechtschaffen et al., 1963; Hishikawa et al., 1976; Mosko et al., 1983), ambulatory (Broughton et al., 1988) and free-run protocols (Pollak and Green, 1990) * Corresponding author. Cattedra di Neurofisiopatologia, DISM, Os- pedale S. Martino, Viale Benedetto XV, 16132, Genoa, Italy. Tel.: +39 10 3537465; Fax: + 39 10 3537699; E-mail: nblino@neurofis.dism.unige. it. have shown a normal total sleep time in narcoleptics. The respective amounts of non-REM (NREM) and REM sleep and the circadian phase of REM sleep are preserved (Baldy-Moulinier et al., 1976). A key feature of th e narcoleptic syndrome is the abnor- mal distribution of sleep and wakefulness over the 24 h (Volk et al., 1990). In narcoleptic subjects the sleep-wake pattern is disrupted by intrusion of sleep during the day and of wakefulness during the night, thus suggesting that narcolepsy could be caused by a disorder of the rhythmic sleep organization resulting from the interaction of homeo- static, circadian and ultradian regulatory processes (Kripke, 1976; Pavel et al., 1980; Mosko et al., 1983). However, it has been shown that a defined circadian pattern persists, albeit attenuated, with most sleep re- stricted to the night period (Broughton et al., 1988; Dantz et al., 1994). In normal subjects circasemidian biorhythms of sleep and wake propensity, expressed by diumal pulses of SWS and forbidden zones for sleep, have been proposed by 0013-4694/95/$09.50 © 1995 Elsevier Science Ireland Ltd. All rights reserved SSDI 001 3-4694(95)0013 8-7 EEG 94763