Polysomnography

Polysomnography (PSG) is the gold-standard multi-channel sleep study conducted in a laboratory setting, simultaneously recording electroencephalography (EEG), electrooculography (EOG), electromyography (EMG), electrocardiography (ECG), respiratory airflow, effort, and oxygen saturation. Sleep stages—N1, N2, N3 (slow-wave), and REM—are scored in 30-second epochs according to the AASM manual using EEG, EOG, and EMG channels. PSG is the reference standard for diagnosing obstructive and central sleep apnea (via apnea-hypopnea index), narcolepsy, REM sleep behavior disorder, and periodic limb movement disorder. Consumer wearables and actigraphy are validated against PSG but typically underestimate N3 and N1 and overestimate sleep efficiency.