What are the main features of NREM sleep?
The current American Academy of Sleep Medicine (AASM) scoring manual for polysomnography revised the Rechtschaffen and Kales (1968) sleep scoring manual, which subdivided NREM sleep into stages 1, 2, 3, and 4.
The current AASM scoring manual designates the sleep stages as the following: N1, N2, N3, and REM. N1 (<5% of total sleep time) is the lightest stage of sleep.
It is distinguished from wakefulness by the absence of alpha rhythm, which is seen in the occipital electroencephalogram (EEG) lead. N2 (40% to 60% of total sleep time) typically follows N1 and is characterized by K-complexes and spindles on EEG.
N3 (10% to 20% of total sleep time in adults, 20% to 40% in children) represents the deeper stages of sleep and is also known as slow-wave sleep or delta sleep for its electroencephalographic characteristics.
The amount of N3 sleep begins decreasing in puberty and continues decreasing into adulthood.
