A 40-year-old woman is found somnolent with her EEG showing high-amplitude, slow-frequency (0.5–2 Hz) waves bilaterally. She is arousable with stimulation, becoming briefly confused before returning to somnolence. Which stage of consciousness does this EEG pattern correspond to, and what is the frequency band involved?
- A Stage N3 (slow-wave sleep); delta waves (0.5–4 Hz)
- B Stupor; delta waves indicating diffuse cortical depression ✓
- C Stage N2 sleep; theta waves (4–8 Hz) with sleep spindles
- D REM sleep; sawtooth theta waves superimposed on low-amplitude mixed-frequency activity
Explanation
The scenario describes stupor: the patient requires vigorous stimulation to arouse, briefly responds, then returns to somnolence. Delta activity (0.5–4 Hz) in a wakeful/pathological context indicates diffuse cortical dysfunction, not normal sleep. Delta waves are normal in stage N3 sleep in healthy individuals, but in a patient being examined clinically who is arousable with stimulation, the same EEG finding represents pathological cortical depression (encephalopathy, metabolic disturbance, or structural lesion). Option A is incorrect because N3 occurs in unresponsive normal sleep, not in someone clinically examined as a patient. Option C describes N2 sleep with spindles and K-complexes. Option D describes REM sleep with low-voltage mixed activity.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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