Overview of EEG Montages and Principles of Localization

Montages are logical, orderly arrangements of electroencephalographic derivations or channels that are created to display activity over the entire head and to provide lateralizing and localizing information. Most often, bipolar and referential montages are used for routine electroencephalographic recordings. Common average and Laplacian montages can also be helpful in some situations. Because each type of montage has certain strengths and limitations, the ACNS guidelines recommend the use of multiple classes of montages for each electroencephalographic recording. A variety of factors need to be considered for localization by scalp electroencephalogram, but in clinical practice, a three-step approach can be used to localize an interictal epileptiform discharge by visual inspection using a standard set of scalp electrodes and conventional montages. The ACNS guideline provides a number of standard and suggested montages, but, depending on the clinical situation, additional montages can be designed using the electrodes within the 10-20 system or by placing additional electrodes.