# Polysomnography

Polysomnography (PSG) is the gold-standard sleep study, done overnight in a lab. It records many channels at once: brain waves (EEG), eye movements (EOG), muscle activity (EMG), heart rhythm (ECG), breathing airflow and effort, and blood oxygen. Sleep stages (N1, N2, N3 deep sleep, and REM) are scored in 30-second chunks, using the EEG, EOG, and EMG, per the AASM manual. PSG is the reference test for diagnosing obstructive and central sleep apnea (via the apnea-hypopnea index), narcolepsy, REM sleep behavior disorder, and periodic limb movement disorder. Consumer wearables and actigraphy are validated against PSG. But they usually underestimate deep (N3) and light (N1) sleep, and overestimate how efficiently you sleep.

## Sources

- Iber C, Ancoli-Israel S, Chesson A, Quan SF (American Academy of Sleep Medicine). (2007). AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications. American Academy of Sleep Medicine
- Rechtschaffen A, Kales A. (1968). A Manual of Standardized Terminology, Techniques and Scoring System for Sleep Stages of Human Subjects. US Government Printing Office

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