Dreaming Sleep in Man: A Reappraisal

Abstract

In man, rapid eye movement (REM) [1] (dreaming sleep) is probably the most interesting of all the stages, by virtue of its phenomena of dreaming, rapid eye movements, loss of muscle tonus, and penile erections, and much of research has been oriented toward it. Even though REM only occupies about 25 percent of total time in adult man, much of the theory and research into function is oriented toward REM. Nevertheless, REM can be considered as a fragile [2] state ofsleep, because in man and in other mammals it tends to be reduced and substituted by light and awakenings whenever such adverse sleeping circumstances as stress, extremes in temperature, or unusual environments are present. Furthermore, nondomestic mammal species living naturaUy under threat of predation have habitually low absolute and relative amounts of REM [2-4], whilst predators tend to have more. This safety factor appears to be independent ofbody size [3]; although it has also been shown that body size itself does influence REM [4]. The fragility and apparent adaptabiUty of REM might suggest that it may not be such a critical type of as is often thought. The aim of the present discussion is to further evaluate this possibility, that despite the intricacies of and the interest paid to REM, its apparent importance may need to be relegated. As will be seen, ofthe remaining human stages, stages 1, 2, 3, and 4 [1], the latter two stages commonly called slow wave sleep (SWS) may be of equal or greater importance to man dian is REM. Although it is generally beueved that REM is oriented toward brain recovery, the discussion also makes the case that there is as yet little firm evidence in supportofthis beliefand that an argument can be made for REM having an energy conserving role for the body. This discussion concerns itself mostly with man, rather than with mammals in general, because it cannot yet be assumed that serves the same functions for all mammals, as differences in cortical develop?DepartmentofHuman Sciences, Loughborough University, Loughborough, Leicestershire, LEU 3TU, England.