I read with great interest the article by Leslie et al .1describing the electroencephalographic correlates of dreaming during anesthesia. Their conclusion that traits of rapid eye movement (REM) sleep are expressed during emergence from anesthesia is provocative. It is of historical interest to note that a common mechanism of dreaming during both sleep and anesthesia was predicted by the psychoanalyst Paul Federn, after the self-analysis of a dream that he experienced under nitrous oxide. Federn discussed this in a 1943 lecture to the American Psychoanalytic Association—one decade before the discovery of REM sleep by Aserinsky and Kleitman2—and, in a later publication, concluded that “one can expect to find the basic mechanisms in dream-production during general anesthesia will not differ from those in dream-production during physiologic sleep.”3 

More modern concepts of relevance to the work by Leslie et al . include “covert REM” and REM sleep as a form of “protoconsciousness.” Nielsen4suggested that isolated REM sleep traits could be expressed during non-REM sleep, thereby accounting for dreaming and mentation during this stage. Therefore, the covert REM hypothesis is consistent with the “simple” anesthesia-related dreams that Leslie et al . describe, which are more characteristic of non-REM dreams despite the electroencephalographic REM-like traits. The framework of covert REM during emergence from anesthesia fits well with the observed data distinguishing the anesthetic dreamer and nondreamer and avoids the need to account for every component of classic REM sleep (e.g ., muscle atonia).

Also of relevance is the suggestion that REM sleep represents a form of protoconsciousness,5a view derived, in part, from the observation that REM sleep occurs during gestation.6The “ontogenetic hypothesis” put forth by Roffwarg et al .7in 1966 suggests that the endogenous process of cortical activation associated with REM sleep prepares the fetus or developing animal for sensory experience. It is of interest to consider whether REM sleep-like traits are a similar form of protoconsciousness that may precede the planned or unplanned emergence from general anesthesia.

University of Michigan Medical School, Ann Arbor, Michigan. gmashour@umich.edu

Leslie K, Sleigh J, Paech MJ, Voss L, Lim CW, Sleigh C: Dreaming and electroencephalographic changes during anesthesia maintained with propofol or desflurane. Anesthesiology 2009; 111:547–55
Aserinsky E, Kleitman N: Regularly occurring periods of eye motility, and concomitant phenomena, during sleep. Science 1953; 118:273–4
Federn P: A dream under general anesthesia. Psychiatr Q 1963; 18:422–38
Nielsen TA: A review of mentation in REM and NREM sleep: “Covert” REM sleep as a possible reconciliation of two opposing models. Behav Brain Sci 2000; 23:851–66
Hobson JA: REM sleep and dreaming: Towards a theory of protoconsciousness. Nat Rev Neurosci 2009; 10:803–13
Birnholz JC: The development of human fetal eye movement patterns. Science 1981; 213:679–81
Roffwarg HP, Muzio JN, Dement WC: Ontogenetic development of the human sleep-dream cycle. Science 1966; 152:604–19