Rapid eye movement sleep and general anesthesia.

To the Editor: I read with great interest the article by Leslie et al. describing 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 Kleitman— 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.” More modern concepts of relevance to the work by Leslie et al. include “covert REM” and REM sleep as a form of “protoconsciousness.” Nielsen suggested 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, a view derived, in part, from the observation that REM sleep occurs during gestation. The “ontogenetic hypothesis” put forth by Roffwarg et al. in 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.