EEG Sleep Staging and Sleep EEG 1 — Questions and Answers
Question 1: Which EEG feature is the hallmark of Stage N2 sleep?
- Sleep spindles and K-complexes (Correct answer)
- Delta waves >75 µV
- Sawtooth waves
- Alpha rhythm dropout
Correct answer: Sleep spindles and K-complexes
Stage N2 sleep is defined by the presence of sleep spindles (12–14 Hz bursts) and K-complexes on EEG.
Question 2: What percentage of total sleep time must be occupied by high-amplitude delta activity to score Stage N3?
- 20%
- 30% or more (Correct answer)
- 50%
- 10%
Correct answer: 30% or more
AASM scoring criteria require that delta waves (0.5–2 Hz, >75 µV) occupy 20% or more of the epoch to score N3, though older criteria used 20% for N3 staging; current AASM requires >20% per epoch.
Question 3: Sawtooth waves during REM sleep are best described as:
- Sharply notched 2–6 Hz theta waves maximal over central regions (Correct answer)
- Spindle bursts at 14 Hz
- High-amplitude delta waves >75 µV
- Rhythmic alpha slowing to 7 Hz
Correct answer: Sharply notched 2–6 Hz theta waves maximal over central regions
Sawtooth waves are notched, sharply contoured theta-range (2–6 Hz) waves seen over central leads during REM sleep.
Question 4: Which sleep stage is characterized by a low-amplitude, mixed-frequency EEG without sleep spindles, K-complexes, or delta waves?
- N1 (Correct answer)
- N2
- N3
- REM
Correct answer: N1
N1 is the lightest NREM stage showing low-voltage, mixed-frequency activity and vertex sharp waves, but lacking spindles and K-complexes.
Question 5: Vertex sharp waves (V-waves) are most prominent during which sleep stage?
- N1 (Correct answer)
- N2
- N3
- REM
Correct answer: N1
Vertex sharp waves are surface-negative transients maximal at Cz that appear during N1 sleep as a normal feature.
Question 6: Muscle atonia on polysomnography is a defining feature of which stage?
- REM sleep (Correct answer)
- N1 sleep
- N2 sleep
- N3 sleep
Correct answer: REM sleep
REM sleep is characterized by active dreaming paired with near-complete skeletal muscle atonia, preventing dream enactment.
EEG Sleep Staging and Sleep EEG 1
Which EEG feature is the hallmark of Stage N2 sleep?