Sleep stages

The REM / NREM ratio

     All warm-blooded mammals have been found to have REM phases during their sleep (I believe that it has now been confirmed that two very primitive animals, the Australian spiny anteater and duck-billed platypus, also have REM phases during their sleep). Whales and dolphins have evolved a very interesting form of sleep which permits them to remain submerged while they rest: one brain hemisphere stays awake and takes care of breathing and movement while the other sleeps and this alternates during the night (Jouvet, 1994, p. 39; Mukhametov et al., 1977). It seems most birds have evolved a similar custom, but in their case it is to keep an eye open for predators (Rattenborg et al., 1999). The length of the sleep cycle seems to be determined by brain mass. Mice have an inter-cycle period of only 9 minutes, while a monkey or child has a period of around 50 minutes (Woods & Greenhouse, 1974, p. 337). Hunters, as one would expect, are able to sleep longer and more peaceably than the hunted (Meier, 1967, p. 39; Woods & Greenhouse, 1974, pp. 336, 341).

     Research has shown that REM/NREM ratio during a night of sleep is independent of the problems, emotional and otherwise, that the dreamer may have, contradicting ideas put forward by Freud and Adler (Woods & Greenhouse, 1974, pp. 288, 303 - 313). It seems the amount of sleep devoted to REM is, however, related to stress and learning (McGrath & Cohen, 1978, pp. 49 - 51). It can also be affected by drugs, as seen in the following table (Woods & Greenhouse, 1974, p. 391; Feinberg et al., 1976):
Drugs (partial list)    Effect on amount of REM sleep
Alcohol decreases
Amphetiamines decreases
Barbiturates decreases
Caffeine none
Chloral hydrate none
Chlorpromazine decreases with small doses
increases with large doses
LSD slight increase
Lithium decreases
Marijuana decreases
Reserpine increases with small doses
decreases with large doses
typtophane increases

     A diagram showing a typical REM/NREM ratio over a lifetime is shown in the next section.

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