1. Double Banana Montage
The most common bipolar montage. It involves two chains of electrodes placed bilaterally along the temporal and parasagittal regions, forming a shape similar to a "double banana." A central chain is placed below the temporal chains.
Limitation: The end of chain phenomenon, where the last electrodes in the chain lack a neighboring electrode for comparison, which can make it harder to interpret certain areas of the brain.
2. Circumferential Montage
Electrodes are arranged in a circle around the head. This arrangement ensures that each electrode has a point of comparison.
Limitation: It does not include many middle or parasagittal electrodes, so it's not ideal for screening EEG tracings. It's generally used to clarify specific discharges or to focus on lateralized activity.
3. T1-T2 Montage
Similar to the double banana but with the parasagittal chains placed at the top. This montage also includes subtemporal electrodes (T1 and T2).
Limitation: Like the double banana, it suffers from the end of chain phenomenon.
4. Transverse Montage
In this montage, the electrode chains are placed side to side rather than front to back. This arrangement is useful for lateralizing brain activity, especially when the dominant hemisphere for a discharge is unclear in a double banana montage.
5. Other Variations
There are also variations and combinations of the montages mentioned above, depending on the specific clinical or diagnostic needs. These can include combinations of the double banana with additional electrodes for more localized recordings or variations that incorporate specific regions of the brain (like occipital or frontal leads) depending on the condition being investigated.