EEG Normal EEG Waveforms 5 — Questions and Answers
Question 1: Which normal EEG feature is defined as a 12–14 Hz waxing-and-waning burst lasting 0.5–3 seconds, maximal over central-parietal regions?
- K-complex
- Sleep spindle (Correct answer)
- Positive occipital sharp transient (POST)
- Vertex sharp wave
Correct answer: Sleep spindle
Sleep spindles are 12–14 Hz (sigma band) bursts with a characteristic spindle shape appearing in stage N2 sleep.
Question 2: Gamma oscillations (>30 Hz) in the normal EEG are most associated with which cognitive state?
- Deep sleep
- High-level cognitive processing and sensory binding (Correct answer)
- Drowsiness
- REM sleep only
Correct answer: High-level cognitive processing and sensory binding
Gamma oscillations are linked to higher cognitive functions such as attention, working memory, and cross-modal sensory binding.
Question 3: A normal adult EEG background shows a well-organized 10 Hz posterior dominant rhythm. This rhythm is categorized as which frequency band?
- Theta
- Alpha (Correct answer)
- Low beta
- Sigma
Correct answer: Alpha
10 Hz falls squarely within the alpha band (8–13 Hz), the normal posterior dominant rhythm of a relaxed, eyes-closed adult.
Question 4: Positive occipital sharp transients of sleep (POSTS) are a normal variant that appear during which sleep stage?
- Stage N1 only
- Stage N2 and N3
- REM sleep only
- Stage N2, N3, and sometimes REM (Correct answer)
Correct answer: Stage N2, N3, and sometimes REM
POSTS are surface-positive sharp transients over the occipital regions seen in stage N2, N3, and sometimes REM sleep.
Question 5: What is the minimum percentage of an epoch that must consist of delta waves for that epoch to be scored as stage N3 sleep?
- 10%
- 20% (Correct answer)
- 50%
- 75%
Correct answer: 20%
By AASM scoring rules, stage N3 requires that delta waves (0.5–2 Hz, >75 µV) occupy at least 20% of a 30-second epoch.
Question 6: The K-complex is a normal EEG feature of stage N2 sleep. What is its characteristic morphology?
- A high-frequency, low-amplitude spindle
- A negative sharp wave followed by a positive slow component, often superimposed by a spindle (Correct answer)
- A series of positive occipital transients
- A monophasic positive deflection at the vertex
Correct answer: A negative sharp wave followed by a positive slow component, often superimposed by a spindle
A K-complex is a well-delineated negative sharp component followed by a positive slow wave, lasting ≥0.5 s, often with a superimposed sleep spindle.
Question 7: In normal neonatal EEGs, which activity pattern is considered developmentally appropriate but would be abnormal in a healthy adult?
- Continuous alpha rhythm
- Trace alternant (burst-suppression-like) pattern during quiet sleep (Correct answer)
- Persistent 14 Hz spindles
- Prominent lambda waves
Correct answer: Trace alternant (burst-suppression-like) pattern during quiet sleep
Trace alternant, characterized by alternating bursts and interburst intervals during quiet sleep, is a normal pattern in full-term neonates up to about 44 weeks conceptional age.
EEG Normal EEG Waveforms 5
Which normal EEG feature is defined as a 12–14 Hz waxing-and-waning burst lasting 0.5–3 seconds, maximal over central-parietal regions?