On EEG, a rhythm of 4-7 Hz is characteristically observed during NREM stage N1 sleep and during hippocampal-dependent memory encoding. This rhythm is best described as:
- A Theta rhythm ✓
- B Beta rhythm
- C Alpha rhythm
- D Delta rhythm
Correct answer: A. Theta rhythm
Explanation
Theta rhythm (4-7 Hz) is characteristic of NREM stage N1 sleep and is also recorded from the hippocampus during memory encoding and spatial navigation. Alpha rhythm (8-13 Hz) is seen in relaxed wakefulness with eyes closed. Beta rhythm (14-30 Hz) occurs during active mental concentration. Delta rhythm (0.5-4 Hz) is seen in deep N3 slow-wave sleep. The key discriminating feature is the 4-7 Hz frequency range.
Reference: Ganong's Review of Medical Physiology, 26th ed.
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