During polysomnography, a patient is noted to have bursts of 12–14 Hz activity lasting 0.5–2 seconds superimposed on a background of K-complexes. Which sleep stage does this pattern represent?

• A Stage N1 (NREM 1)
• B Stage N2 (NREM 2) ✓
• C Stage N3 (NREM 3 / slow-wave sleep)
• D REM sleep

Explanation

Stage N2 sleep is characterised by two hallmark EEG features: sleep spindles (bursts of 12–14 Hz sigma activity lasting 0.5–2 seconds generated by thalamo-cortical circuits) and K-complexes (high-amplitude biphasic slow waves often triggered by external stimuli). N3 shows high-amplitude delta waves (0.5–2 Hz, >75 µV) occupying >20% of the epoch. REM shows low-amplitude mixed-frequency activity resembling the waking EEG.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.