... refers to the amount of oscillations per second and so is demonstrated in the graph by shorter wave-lengths. Physiologists such as Aserinsky and Kleitman in 1953 found that using this technique on sleeping subjects could give an insight into the state of the brain during stages of unconsciousness. It was through this that they identified two 'classes' of sleep. These were named slow-wave sleep (SWS) and rapid eye movement sleep (REM). The first has 4 subcategories, all identifiable by differing frequencies and amplitudes of oscillations on the EEG reading. Each of these stages has a specific range, measured in hertz (Hz), in order to aid identification. In this case the EEG technique was used to separate sleep into stages. The first stage of SWS is characterised by the 'alpha rhythm' which occurs when the subject is awake but relaxed with their eyes shut, limiting the input of sensory stimuli. It ranges ...

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