Montages

The word montage simply refers to the pattern of EEG collection activity with respect to the electrodes. It is the method of collecting and representing the EEG amplifier channels. In medical qEEG montages emerged, such as the banana montage, in response to searches for EEG features of a specific nature such as a lesion of seizure source. An EEG voltage signal represents a difference between the voltages at two electrodes and consequently the display of the EEG for the clinician may be set up in one of several ways. The primary two ways used in neurofeedback are monopolar, or linked ears montage, and bipolar montage.

Bipolar Montage

Each channel represents the difference between two adjacent electrodes and the entire montage will consist of a series of these channels. For example, the channel "Fp1-F3" represents the difference in voltage between the Fp1 electrode and the F3 electrode. The next channel in the montage, "F3-C3," represents the voltage difference between F3 and C3, and so on through the entire array of electrodes. In neurofeedback, we usually use only one or two channels that employ a bipolar montage.

Referential Montage

Each channel in this montage represents the difference between a certain electrode and a designated reference electrode. There is no standard position for this reference, but it is at a different position than the "recording" electrodes. Midline positions are often used because they do not amplify the signal in one hemisphere vs. the other. Another popular reference is "linked ears," which is a physical or mathematical average of electrodes attached to both earlobes. This is the montage used in qEEG because this is how the data was originally collected for the databases. A great deal of analysis and thought went into deciding on a reference point for neurometrics and E Roy John wrote quite extensively on the topic.

Average Reference Montage

In this montage, the outputs of all of the amplifiers are summed and averaged, and this averaged signal is used as the common reference for each channel. Weighted averages or Laplacian analysis, described previously, is the method commonly used in qEEG databases presently but some research databases, such as Neuroguide, allow for any combination of electrode analysis.

Montages

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