Britannica Sources used in this answer

Why is N3 considered the deepest stage of NREM sleep?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Hear how scientists are studying the sleep-related brain activity of animals and migratory birds — sleep Find out how scientists are studying the sleep activity of migratory birds.

N3 is considered the deepest stage of NREM sleep because it is characterized by the predominance of high-amplitude, low-frequency brain waves known as slow waves.12

In electroencephalography (EEG) monitoring, N3 is defined as the point at which these slow waves occupy more than 20 percent of a 30-second window. Due to this defining feature, N3 is frequently referred to as slow-wave sleep (SWS). These EEG patterns are associated with a state of significantly decreased vigilance, meaning the brain shows reduced alertness to immediate or critical external events.12

As sleep progresses from the lighter N1 and N2 stages, slow-wave activity becomes increasingly abundant, marking the transition into this deeper, more restful state. This stage is associated with a decrease in the activity of the autonomic nervous system and reduced average brain activity, particularly in the thalamus and frontal cortex, which supports the theory that N3 plays a vital role in the body's recuperative and restorative functions.12