EEG Normal EEG Waveforms 4 — Questions and Answers
Question 1: Which EEG frequency band is most prominent during deep NREM sleep (stage N3)?
- Delta (0.5–4 Hz) (Correct answer)
- Theta (4–8 Hz)
- Alpha (8–13 Hz)
- Beta (13–30 Hz)
Correct answer: Delta (0.5–4 Hz)
Stage N3 (slow-wave sleep) is defined by high-amplitude delta waves occupying at least 20% of the epoch.
Question 2: What is the typical voltage (amplitude) range of normal alpha waves recorded from the scalp?
- 5–10 µV
- 20–200 µV (Correct answer)
- 200–500 µV
- 500–1000 µV
Correct answer: 20–200 µV
Alpha waves normally range from about 20 to 200 µV in amplitude when recorded from scalp electrodes.
Question 3: The 'mu rhythm' seen over the central scalp in a relaxed, awake subject has a frequency overlapping with which other rhythm?
- Delta
- Theta
- Alpha (Correct answer)
- Gamma
Correct answer: Alpha
The mu rhythm (8–13 Hz) overlaps the alpha frequency band but is maximal over central (C3/C4) rather than occipital electrodes.
Question 4: During hyperventilation in a normal adult, what EEG change is expected?
- Increased beta activity
- Increased high-amplitude slow activity (Correct answer)
- Complete EEG suppression
- Onset of sleep spindles
Correct answer: Increased high-amplitude slow activity
Hyperventilation causes cerebral vasoconstriction and hypocapnia, producing diffuse high-amplitude slow (delta/theta) activity in normal subjects.
Question 5: Which waveform is considered a normal variant and is characteristically seen at the vertex during stage N1 sleep?
- K-complex
- Vertex sharp wave (Correct answer)
- Sleep spindle
- Lambda wave
Correct answer: Vertex sharp wave
Vertex sharp waves (V-waves) are normal, high-amplitude transients maximal at Cz that appear during drowsiness and stage N1 sleep.
Question 6: Lambda waves in the EEG are best elicited by which condition?
- Eye closure in a dark room
- Active visual scanning of a patterned surface (Correct answer)
- Auditory stimulation
- Voluntary limb movement
Correct answer: Active visual scanning of a patterned surface
Lambda waves are positive occipital transients that occur during active visual scanning (saccadic eye movements) of a patterned scene.
Question 7: In a normal adult EEG, what is the expected effect of opening the eyes on the posterior alpha rhythm?
- Alpha amplitude increases
- Alpha is attenuated or blocked (Correct answer)
- Alpha frequency increases by 4 Hz
- Alpha spreads to frontal regions
Correct answer: Alpha is attenuated or blocked
Eye opening causes alpha blocking (Berger effect), suppressing posterior alpha due to visual cortex activation.
EEG Normal EEG Waveforms 4
Which EEG frequency band is most prominent during deep NREM sleep (stage N3)?