Polysomnography
Polysomnography (PSG) is a test used in the study of sleep; the test result is called a polysomnogram. Below are images of the NREM stages 1, 2 and 4 (prior to the merging of stages 3 and 4).
The figures represent 30-second epochs (30 seconds of data). They represent data from both eyes, chin, EEG, legs, microphone, intercostal EMG, sternocleidomastoid activity, nasal/oral air flow, thoracic effort, abdominal effort, EKG, oxymetry, and body position, in that order. EEG is highlighted by the red box. Sleep spindles in the stage 2 figure are underlined in red.
Stage 1:
Read more about this topic: Non-rapid Eye Movement Sleep