Prior to this the Rechtschaffen and Kales (RK) rules were used to classify sleep stages. There is a protocol defined by the American Academy of Sleep Medicine (AASM) for sleep scoring, whereby the sleep or wake state is recorded in 30-second epochs. Certain frequencies displayed by EEGs, EOGs and EMGs are characteristic and determine what stage of sleep or wake the subject is in. The output from these three sources is recorded simultaneously on a graph by a monitor or computer as a hypnogram. Hypnograms are usually obtained by visually scoring the recordings from electroencephalogram (EEGs), electrooculography (EOGs) and electromyography (EMGs). Method A hypnogram (top) with other readings below The previously considered 4th stage of NREM sleep has been included within stage 3 this stage is also called slow wave sleep (SWS) and is the deepest stage of sleep. NREM sleep can be further classified into NREM stage 1, 2 and 3. It allows the different stages of sleep: rapid eye movement sleep (REM) and non-rapid eye movement sleep (NREM) to be identified during the sleep cycle. It was developed as an easy way to present the recordings of the brain wave activity from an electroencephalogram (EEG) during a period of sleep. Here, both stage 3 and stage 4 are shown these are often combined as stage 3.Ī hypnogram is a form of polysomnography it is a graph that represents the stages of sleep as a function of time. Graph of a person's sleep Example hypnogram of a normal, healthy adult
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