EEG Electrode Placement and Montages 5 — Questions and Answers
Question 1: Which montage type is most useful for localizing the PHASE REVERSAL of an epileptiform discharge?
- Bipolar montage (Correct answer)
- Referential montage
- Laplacian montage
- Average reference montage
Correct answer: Bipolar montage
Bipolar montages are best for localizing epileptiform discharges because phase reversals occur at the electrode directly over the focus.
Question 2: In the revised IFCN electrode nomenclature, electrode T5 is now called:
- P7 (Correct answer)
- T7
- P5
- TP7
Correct answer: P7
In the revised nomenclature, T5 was renamed P7 because it overlies the posterior temporal/parietal region, not the mid-temporal region.
Question 3: A technologist notices a phase reversal at F7 in a bipolar montage. What does this indicate?
- Maximum electrical activity at F7 (Correct answer)
- Minimum electrical activity at F7
- F7 is the reference electrode
- The montage chain is incorrectly ordered
Correct answer: Maximum electrical activity at F7
In a bipolar montage, phase reversal at a specific electrode indicates that the maximum (or focus of) electrical activity is located at that electrode.
Question 4: How many electrodes are used in the standard 10-20 system?
- 21 (Correct answer)
- 19
- 25
- 16
Correct answer: 21
The standard 10-20 system uses 21 electrodes, including 19 scalp electrodes plus A1 and A2 ear reference electrodes.
Question 5: Which electrode site is used as the nasion landmark in the 10-20 measurement system?
- The bridge of the nose between the eyes (Correct answer)
- The tip of the nose
- The center of the forehead
- The glabella above the nose
Correct answer: The bridge of the nose between the eyes
The nasion is the depression at the bridge of the nose between the eyes and serves as the anterior skull landmark for 10-20 measurements.
Question 6: In a circumferential (transverse) bipolar montage, electrodes are chained:
- Around the head from left to right across the coronal plane (Correct answer)
- From front to back along the sagittal plane
- From each scalp electrode to a common reference
- From temporal to occipital electrodes only
Correct answer: Around the head from left to right across the coronal plane
A transverse (circumferential) bipolar montage chains electrodes in a left-to-right order across the coronal plane, running from one side of the head to the other.
Question 7: What is the primary advantage of using an average reference montage?
- It reduces bias from any single reference electrode location (Correct answer)
- It best localizes focal epileptiform discharges
- It eliminates the need for impedance checks
- It reduces the number of electrodes required
Correct answer: It reduces bias from any single reference electrode location
The average reference montage uses the average of all electrodes as the reference, which reduces the distortion that can occur when a single reference electrode is near active brain tissue.
EEG Electrode Placement and Montages 5
Which montage type is most useful for localizing the PHASE REVERSAL of an epileptiform discharge?