What mysteries does the reference electrode hide?

Abstract

The reference electrode is an integral part in each electroencephalographic (EEG) derivation involved in recording montage. In the era of ink-writing EEG devices, contact between the active and reference EEG electrodes was established manually using special switches. Now, with the advent of computer electroencephalographs, EEG leads are formed not only at the hardware level, but also at the software level. Several types of reference electrodes have emerged: ear, central, averaged, combined ear, Laplace reference, etc. It is not surprising to get confused in such abundance. This publication details a role for active and passive (reference) electrodes, introduce the concept of EEG derivation, recording montage as well as dissects the differences between hardware and software reference electrodes. A proper understanding of how EEG equipment operates at the level of active and reference electrodes may help medical personnel in its correct set up and interpreting EEG examinations data.