Electrode Placement and Montages Flashcards

In the International 10-20 system, what do the numbers 10 and 20 represent?

Answer: The percentage of distance between skull landmarks for electrode placement

The 10-20 system places electrodes at 10% and 20% intervals of the measured distances between standardized skull landmarks (nasion, inion, preauricular points).

Which montage type displays the voltage difference between each electrode and a common reference point?

Answer: Referential montage

A referential montage shows the potential at each electrode compared to a single common reference (such as linked ears, Cz, or an average reference), allowing direct comparison of amplitudes across channels.

In a bipolar longitudinal (anterior-posterior) montage, a phase reversal at C3 indicates:

Answer: Maximum negativity or positivity at C3

A phase reversal occurs where adjacent channels sharing an electrode deflect in opposite directions, indicating the electrode at the reversal point has the maximum voltage for that event.

The electrode labeled 'Fz' in the 10-20 system is located at:

Answer: The midline frontal position

The 'z' designation indicates a midline position. Fz (frontal zero) is the midline frontal electrode positioned at 30% of the nasion-to-inion distance from the nasion.

What is the maximum recommended electrode impedance for routine EEG recording according to ACNS guidelines?

Answer: 5 kOhm

The American Clinical Neurophysiology Society recommends electrode impedances be below 5 kOhm and balanced across all electrodes to optimize signal quality and common-mode rejection.

An average reference montage calculates each channel's display by:

Answer: Subtracting the computed average of all electrode voltages from each electrode

The average reference uses the arithmetic mean of all active electrodes as the reference point. Each channel displays the difference between one electrode and this common average, providing a relatively neutral reference.