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Sleep researchers must grapple with a major conundrum: we don’t really know what sleep is. This may come as a shock to the uninitiated, but a conclusive definition of sleep still eludes scientists and probably will continue to do so until the function of sleep is fully established. That’s not to say science doesn’t have a working definition of sleep.
Researchers have used electrophysiology to characterize sleep since the middle of the 20th century. In animals with a developed neocortex, including mammals and birds, sleep states manifest as telltale patterns of brain activity, which can be detected by electroencephalography (EEG), along with distinct eye movements and changes in muscle tone. Rapid eye movement (REM) sleep and non-REM sleep are differentiated by behavioral attributes and characteristic ...