1957 W. Dement & N. Kleitman in 53 340/1 In most of the remaining text the following abbreviations will be used: REM's (rapid eye movements) and NREM's (no rapid eye movements).
1974 V. B. Mountcastle et al. (ed. 13) I. viii. 280/2 REM sleep and NREM sleep in narcolepsy and hypersomnia.
1996 D. J. Weatherall et al. (ed. 3) II. xvii. 2906/2 NREM sleep shows a continuum from drowsy right down to very deep sleep.