| nREM and REM: Sleep types |
| By Darien Simon |
| For most of the 20th century it was known that sleeping people passed through different stages of sleep during the night. But it wasn’t until the 1950s that research on sleep, sleep stages, and dreaming began to make real progress in understanding what happens during sleep. In 1952 Drs. Aserinsky and Kleitman, who were studying infants, noted the phenomenon that has come to be known as “rapid eye movement” and associated this movement with a particular stage of sleep, called “REM sleep” or stage 5 sleep, for this characteristic jerky movement of the eye muscles. The other 4 stages of sleep are all considered non-rapid eye movement sleep or nREM sleep [LINK: nREM Sleep—stages 1 – 4]. Additional research discovered there are different brain wave patterns characteristic of different stages of sleep, along with physiological changes that can be measured by electroencephalographs, electromyographs, and other instruments that are combined into a form of measurement called polysomnography (multiple sleep measure) [LINK: TBW]. It has also been discovered that both nREM and REM sleep are not unique to humans, but occur in mammals and birds, and may be found in somewhat altered forms in reptiles, though the evidence for that is less clear and consistent than for other animals. Anyone with a pet cat or dog might have observed their pet occasionally showing signs of REM sleep such as jerking movements of extremities (especially paws) and the rapid movements of muscles immediately around the eyes. Unlike humans and domestic animals, some animals may have very different behaviors or postures depending on what stage of sleep they are in. For example, elephants in nREM stages sleep standing up, while they lie down for REM sleep. There have been reports that dolphins do not experience REM sleep after birth, however, the evidence for this claim is inconclusive. Of the two main types of sleep, REM sleep is most closely associated with dreaming, especially with intense and vivid dreams. However, people apparently do dream during nREM sleep as well. Most importantly, both types of sleep are necessary to a good night’s sleep, because they apparently serve different functions, though what the exact purpose of each type or stage of sleep is, has not yet been determined. |
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