States and stages of human sleep are defined on the basis of characteristic patterns in all of the following except:

States and stages of human sleep are defined on the basis of characteristic patterns in the electroencephalogram (EEG), the electrooculogram (EOG—a measure of eye-movement activity), and the surface electromyogram (EMG) measured on the chin and neck. The continuous recording of this array of electrophysiologic parameters to define sleep and wakefulness is termed polysomnography. Polysomnographic profiles define two states of sleep: (1) rapid-eye-movement (REM) sleep and (2) nonrapid-eye-movement (NREM) sleep. NREM sleep is further subdivided into three stages, characterized by increasing arousal threshold and slowing of the cortical EEG. REM sleep is characterized by a low amplitude, mixed-frequency EEG similar to that of NREM stage N1 sleep. The EOG shows bursts of REM similar to those seen during eyes-open wakefulness. Chin EMG activity is absent, reflecting the brainstem mediated muscle atonia that is characteristic of that state.