EEG is used in polysomnography(PSG), which is a sleep study performed overnight while being continuously monitored by a credentialed technologist. many information can be extrapolated from the polysomnography; some can be directly related to the sleep, such as the sleep onset latency (SOL), the REM-sleep onset latency, the number of awakenings during the sleep-period, the total sleep duration, percentages and durations of every sleep stage, and the number of arousals. Polysomnography is used to diagnose, or rule out, many types of sleep disorders, including narcolepsy, idiopathic hypersomnia, periodic limb movement disorder (PLMD), REM behavior disorder, parasomnias, and sleep apnea.