Referential montages in electroencephalography (EEG) are a method of electrode placement where all electrodes are referenced to a single reference point, rather than to each other as in bipolar montages. This reference point can be chosen in several ways, but the most common choices are:
- Average Montage: The reference is the average voltage of all electrodes.
- Ear Reference: The reference is often one of the electrically neutral points, such as the auricle (ear).
Key Characteristics of Referential Montages:
- Single Reference Point: All EEG channels are compared to this one reference point, instead of between two adjacent electrodes.
- Simpler Interpretation: In a referential montage, waves are categorized simply: upward waves are considered negative, and downward waves are positive, with no phase reversals. This makes it easier to identify the highest amplitude signal.
- No Phase Reversals: Unlike bipolar montages, which can display phase reversals that help highlight certain events (like epileptiform discharges), referential montages do not exhibit phase reversals, which can make detecting these discharges harder.
Benefits:
- Clear Identification of Maximal Voltage: Referential montages help easily identify the point of maximal voltage in the EEG trace.
- Simpler for Certain Analyses: The straightforward nature of referential montages makes them useful when trying to assess the overall amplitude of brain activity.
Drawbacks:
- Reduced Sensitivity for Epileptiform Activity: The lack of phase reversals in referential montages makes it harder to detect subtle abnormal brain activity, like seizures or other epileptiform discharges, which are more easily identified with bipolar montages.
In summary, referential montages are valuable for studying the overall voltage distribution in the brain, but they can be less sensitive to certain kinds of abnormal electrical activity compared to bipolar montages.