An EEG recorded while a healthy adult is drowsy but awake shows rhythmic waves of 4 to 7 Hz over the temporal regions. Which rhythm is this, and where is it most prominently generated?
- A Alpha rhythm, generated in the occipital cortex
- B Delta rhythm, generated in the thalamus
- C Theta rhythm, prominent over the hippocampus ✓
- D Mu rhythm, generated in the motor cortex
Correct answer: C. Theta rhythm, prominent over the hippocampus
Explanation
Theta activity of 4 to 7 Hz appears normally during drowsiness and light meditation and is the dominant rhythm arising from the hippocampus. Alpha is 8 to 13 Hz occipital and reacts to eye opening, delta is under 4 Hz and marks deep sleep or pathology, and mu is a 7 to 11 Hz arciform rhythm over sensorimotor cortex that blocks with limb movement, not with eye closure.
Reference: Ganong's Review of Medical Physiology, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.