Consciousness and Cognition 9, 488–509 (2000) doi:10.1006/ccog.2000.0466, available online at http://www.idealibrary.com on REM Mentation in Narcoleptics and Normals: An Empirical Test of Two Neurocognitive Theories Roar Fosse Institute of Psychology, University in Oslo, Oslo, Norway This study tested the two main neurocognitive models of dreaming by using cognitive data elicited from REM sleep in normals and narcoleptics. The two models were the ‘‘acti- vation-only’’ view which holds that, in the context of sleep, overall activation of the brain is sufficient for consciousness to proceed in the manner of dreaming (e.g., Antrobus, 1991; Foulkes, 1993; Vogel, 1978); and the Activation, Input source, Modulation (AIM model), which predicts that not only brain activation level but also neurochemical modulatory sys- tems exert widespread effects upon dreaming (Hobson & McCarley, 1977; Hobson, Pace- Schott, & Stickgold, 2000). Mental activity was studied in nocturnal REM in 15 narcolep- tics and 9 normal healthy persons and in REM at the onset of daytime naps and nighttime sleep (SOREM) in narcoleptics. The study was performed in the subjects’ homes, using instrumental awakenings and ambulatory polysomnographic techniques, and focused upon visual vividness, mentation report length, improbable and discontinuous bizarre features, and reflective consciousness. Within each subject group, most cognitive variables tended to fluctuate in line with expected variations in circadian activation level. When comparing the cognitive variables between the two groups, reflective consciousness was clearly high- est in narcoleptics, whereas improbabilities and discontinuities were lower, with mentation report length and visual vividness differing less between the groups. These findings are consistent with the AIM model of sleep mentation, but not with the activation-only model.  2000 Academic Press INTRODUCTION A major dispute in dream science over the past two decades has concerned what sorts of brain processes are crucial for the universal, formal characteristics of mental activity during sleep. Several researchers (Antrobus, 1986; 1991; Foulkes, 1993, 1996, 1999; Moffitt, 1995; Vogel, 1978; Zimmerman 1970) have argued that, when combined with the characteristic reduction or blockade of external stimuli (Coenen, 1998), activation of cognitive and cerebral processes in sleep is all that is required for consciousness to proceed in the nondirected manner of dreaming. Antrobus (1986, 1990, 1991, 1993) has expressed this ‘‘activation-only’’ view in neurocognitive terms in previous versions of his general cortical activation and high threshold (GCAT) model. In this model, the 24-h (circadian) activation–deactivation cycle and the ultradian REM– N(on) REM cycle are seen to contribute in an additive manner to the general level The author thanks Khalil Kayed, Ivar Reinvang, J. Allan Hobson, Edward F. Pace-Schott, Robert Stickgold, John S. Antrobus, Dag-Erik Eilertsen, Magdalena J. Fosse, Paal Helge Groenhaug, the staff at the Akershus Central Hospital Sleep Laboratory, and last, but not the least, the participants. Address correspondence and reprint requests to Roar Fosse, Department of Psychology, University of Oslo, P. O. Box 1094 Blindern, N-0317 Oslo, Norway. E-mail: roar.fosse@psykologi.uio.no. 488 1053-8100/00 $35.00 Copyright  2000 by Academic Press All rights of reproduction in any form reserved.