During stage N3 (slow-wave sleep), which EEG pattern predominates, and what is its frequency range?
- A Alpha waves: 8–13 Hz
- B Theta waves: 4–7 Hz
- C Delta waves: <2 Hz, amplitude >75 µV, occupying >20% of epoch ✓
- D K-complexes and sleep spindles: 12–14 Hz
Correct answer: C. Delta waves: <2 Hz, amplitude >75 µV, occupying >20% of epoch
Explanation
Stage N3 (deep NREM sleep, previously stages 3 and 4) is defined by the presence of high-amplitude delta waves (<2 Hz, amplitude >75 µV) comprising more than 20% of the epoch. This stage is also called slow-wave sleep (SWS) or restorative sleep; growth hormone secretion peaks during N3. Sleep spindles and K-complexes characterize stage N2, while alpha waves are the hallmark of quiet wakefulness with eyes closed.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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