During which stage of sleep does the highest threshold for arousal typically occur, and what EEG pattern characterises this stage?
- A Stage N3 (slow-wave sleep); delta waves (0.5–4 Hz) comprising >20% of the epoch ✓
- B REM sleep; low-voltage mixed-frequency 'sawtooth' waves
- C Stage N2; sleep spindles (12–15 Hz) and K-complexes
- D Stage N1; theta waves and slow rolling eye movements
Correct answer: A. Stage N3 (slow-wave sleep); delta waves (0.5–4 Hz) comprising >20% of the epoch
Explanation
Stage N3 (slow-wave sleep, SWS) is the deepest NREM stage, characterised by high-amplitude delta waves (0.5–4 Hz) occupying more than 20% of a 30-second epoch. It has the highest arousal threshold — people are most difficult to awaken from N3. REM sleep (option B) paradoxically has a lower arousal threshold in many contexts, and its EEG resembles wakefulness with additional sawtooth waves. N2 (option C) features sleep spindles and K-complexes; N1 (option D) is the lightest sleep stage with theta waves.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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