<p><span>An EEG montage is the placement of electrodes. All EEG signals are measured by subtracting the signal measured at 2 sites: the active electrode and the reference electrode.&nbsp; This is called common mode rejection.&nbsp; The reason for this is that we need to subtract out all the environmental electrical noise (which is much larger than the brainwave signal) in order to see the brain's activity.&nbsp; Any scalp electrode site measurement must be referenced to some other measured site.&nbsp; In the past, the most common site for reference was linked ears.&nbsp; But you can use the nose, or any other scalp location or, as explained above, any average of multiple sites.&nbsp; So, there are many montages available and they all have strengths and weaknesses.&nbsp; There is no best montage for all purposes.</span></p>