RPSGT RPSGT Electroencephalography & Signal Interpretation 5 — Questions and Answers
Question 1: POSTS (positive occipital sharp transients of sleep) are normal EEG variants seen during which stage?
- N3 sleep
- REM sleep
- N1 and N2 sleep (Correct answer)
- Wakefulness only
Correct answer: N1 and N2 sleep
POSTS are normal, benign waveforms seen in N1 and N2 sleep, maximal over occipital regions, and should not be mistaken for pathology.
Question 2: The international 10-20 electrode placement system derives its name from the fact that electrodes are placed at intervals of:
- 10 mm and 20 mm apart
- 10% and 20% of skull circumference distances (Correct answer)
- 10 and 20 microvolts apart
- 10 Hz and 20 Hz frequency bands
Correct answer: 10% and 20% of skull circumference distances
The 10-20 system spaces electrodes at 10% and 20% intervals of the total skull circumference measured in each plane.
Question 3: A patient's EEG shows continuous, diffuse high-amplitude delta activity throughout an entire overnight study. This pattern is most consistent with:
- Normal Stage N3 sleep throughout
- Severe encephalopathy or deep coma (Correct answer)
- REM behavior disorder
- Idiopathic hypersomnia
Correct answer: Severe encephalopathy or deep coma
Continuous diffuse delta without normal sleep architecture cycling suggests severe cerebral dysfunction such as encephalopathy or coma.
Question 4: Which filter setting in PSG is specifically used to reduce slow-moving artifacts such as sweat and movement?
- High-frequency filter (HFF)
- Low-frequency filter (LFF) / High-pass filter (Correct answer)
- Notch filter at 60 Hz
- Band-stop filter at 0.5 Hz
Correct answer: Low-frequency filter (LFF) / High-pass filter
The low-frequency filter (high-pass filter) attenuates very slow frequencies, reducing sweat and movement artifacts that appear as slow undulations.
Question 5: K-complexes on EEG must have a total duration of at least:
- 0.25 seconds
- 0.5 seconds (Correct answer)
- 1.0 second
- 2.0 seconds
Correct answer: 0.5 seconds
By AASM definition, a K-complex is a well-delineated negative sharp wave followed by a positive component with total duration ≥0.5 seconds.
Question 6: In a bipolar EEG derivation, if the potential at electrode A is +50 µV and at electrode B is +20 µV, the recorded deflection will be:
- +70 µV upward deflection
- +30 µV deflection reflecting A minus B (Correct answer)
- +30 µV deflection reflecting B minus A
- No deflection because both are positive
Correct answer: +30 µV deflection reflecting A minus B
Bipolar recording subtracts the second electrode from the first (A − B), yielding +30 µV; the polarity convention determines deflection direction.
Question 7: Sleep spindles are generated primarily by thalamo-cortical circuits and are typically recorded at maximum amplitude over which scalp region?
- Occipital (O1, O2)
- Frontal (Fp1, Fp2)
- Central (C3, C4) (Correct answer)
- Temporal (T3, T4)
Correct answer: Central (C3, C4)
Sleep spindles are maximal over central scalp regions because of their thalamocortical origin projecting to sensorimotor cortex.
RPSGT RPSGT Electroencephalography & Signal Interpretation 5
POSTS (positive occipital sharp transients of sleep) are normal EEG variants seen during which stage?