Hypnogram

A hypnogram is a form of polysomnography; it is a graph that represents the stages of sleep as a function of time.

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.

[1] Hypnograms are usually obtained by visually scoring the recordings from electroencephalogram (EEGs), electrooculography (EOGs) and electromyography (EMGs).

Certain frequencies displayed by EEGs, EOGs and EMGs are characteristic and determine what stage of sleep or wake the subject is in.

[8] Hypnograms for healthy persons vary slightly according to age, emotional state, and environmental factors.

[13] The method of obtaining the data used in a hypnogram is restricted to the input from an EEG, EOG or EMG.

[14] Another advancement involves combining hypnograms with color density spectral arrays to improve the quality of sleep analysis.

Example hypnogram for a normal, healthy adult. Within the first hour of sleep SWS is displayed. Cycles of REM and NREM sleep proceed. During the third cycle of sleep there are two brief wake states. During the second half of the sleep period more REM sleep is displayed and there is little SWS detected.
Example hypnogram of a normal, healthy adult
Here, both stage 3 and stage 4 are shown; these are often combined as stage 3.
A hypnogram (top) with other readings below