A polysomnography technician notes transient, sharply contoured negative-positive deflections maximal at the vertex electrodes occurring singly against a low-amplitude mixed-frequency background with slow eye movements. Which sleep stage does this epoch represent?

• A REM sleep
• B Stage N2
• C Stage N3
• D Stage N1 ✓

Explanation

Vertex sharp waves together with low-amplitude mixed-frequency EEG and slow rolling eye movements define stage N1, the transitional stage between wakefulness and deeper sleep. Stage N2 requires spindles or K-complexes, N3 requires slow-wave activity in 20 percent or more of the epoch, and REM requires muscle atonia plus rapid eye movements, so none of those criteria are met here.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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