EEG Electrode Placement and Montages 4 — Questions and Answers
Question 1: In the 10-20 system, which electrode is located at the vertex of the skull?
- Cz (Correct answer)
- Pz
- Fz
- C3
Correct answer: Cz
Cz is located at the vertex (top) of the skull at the intersection of the midline and a line connecting the two ears.
Question 2: What does a referential montage compare each electrode to?
- A common reference electrode (Correct answer)
- The adjacent electrode
- The opposite hemisphere electrode
- The ground electrode
Correct answer: A common reference electrode
In a referential montage, each active electrode is compared to a single common reference electrode, often placed at the ear or linked mastoids.
Question 3: Which electrode placement best captures activity from the temporal lobe?
- T3/T4 (T7/T8) (Correct answer)
- F3/F4
- P3/P4
- O1/O2
Correct answer: T3/T4 (T7/T8)
T3/T4 (now called T7/T8 in the revised system) are positioned over the temporal lobes and best capture temporal lobe activity.
Question 4: What is the purpose of the ground electrode in an EEG recording?
- To reduce common-mode noise and electrical interference (Correct answer)
- To serve as the primary reference
- To detect eye movement artifacts
- To measure impedance across the scalp
Correct answer: To reduce common-mode noise and electrical interference
The ground electrode helps the amplifier reject common-mode noise and electrical interference by providing a reference point for the differential amplifier.
Question 5: In a bipolar longitudinal montage, what is the typical chain order for the left hemisphere?
- Fp1-F3-C3-P3-O1 (Correct answer)
- O1-P3-C3-F3-Fp1
- Fp1-F7-T3-T5-O1
- F3-C3-P3-T3-O1
Correct answer: Fp1-F3-C3-P3-O1
The standard longitudinal bipolar (double banana) chain runs from front to back: Fp1-F3-C3-P3-O1 for the left parasagittal chain.
Question 6: Which statement about electrode impedance is correct for clinical EEG?
- Impedance should be below 5 kΩ for optimal recording (Correct answer)
- Higher impedance improves signal quality
- Impedance above 20 kΩ is acceptable
- Impedance only affects artifact, not signal amplitude
Correct answer: Impedance should be below 5 kΩ for optimal recording
Electrode impedance should be below 5 kΩ (ideally 1-5 kΩ) to ensure adequate signal quality and minimize noise artifacts.
Question 7: What does the '10' and '20' refer to in the International 10-20 system?
- Percentage of total skull distance between electrode sites (Correct answer)
- Millimeters between electrodes
- Number of electrodes in each region
- Frequency bands measured at each site
Correct answer: Percentage of total skull distance between electrode sites
The 10 and 20 refer to the percentage of the total front-to-back or left-to-right skull distance used as the spacing between electrode positions.
EEG Electrode Placement and Montages 4
In the 10-20 system, which electrode is located at the vertex of the skull?