A patient's EEG shows a rhythm of 8–13 Hz over the posterior cerebral regions that disappears when the patient opens their eyes. This rhythm is best described as:
- A Alpha rhythm — dominant awake-relaxed rhythm that is attenuated by visual input ✓
- B Beta rhythm — high-frequency rhythm associated with mental activity
- C Theta rhythm — drowsiness rhythm seen in temporal regions
- D Mu rhythm — sensorimotor rhythm attenuated by movement intention
Correct answer: A. Alpha rhythm — dominant awake-relaxed rhythm that is attenuated by visual input
Explanation
Alpha waves (8–13 Hz) are the dominant EEG pattern in awake, relaxed adults with eyes closed, maximal in the parieto-occipital regions. Eye opening causes alpha-blocking (Berger's phenomenon) due to visual cortex activation. Beta waves (option B; >13 Hz) are associated with active thinking and are frontally prominent. Theta waves (option C; 4–7 Hz) occur during drowsiness or temporal lobe activity. Mu rhythm (option D) is a 8–12 Hz sensorimotor rhythm suppressed by actual or imagined movement, not by eye opening.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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Written and medically reviewed by the StethoPrep medical team.