During overnight polysomnography, K-complexes and sleep spindles are observed. These electrophysiological features are characteristic of which stage of NREM sleep?
- A Stage N2 ✓
- B Stage N1
- C Stage N3
- D Stage R
Correct answer: A. Stage N2
Explanation
Stage N2 sleep is defined by the presence of sleep spindles (11-16 Hz bursts) and K-complexes (high-amplitude biphasic waves) on EEG. Stage N1 shows theta activity and vertex sharp waves. Stage N3 (slow-wave sleep) shows delta waves. Stage R is REM sleep with low-amplitude mixed-frequency activity.
Reference: Ganong's Review of Medical Physiology, 26th ed.
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