3 - Connecting Electrodes to Amplifiers

Abstract

This chapter focuses on connecting electrodes to amplifiers. A partial solution to measure the distribution of electrical potential over the scalp is achieved by the choice of appropriate methods of connecting the scalp electrodes to the recording amplifiers. There are three basic methods of deriving electrical signals from an electrode array. These are bipolar, unipolar, and average reference methods. In the bipolar method, each channel is connected between two electrodes both of which are likely to be affected by appreciable electroencephalogram potentials. The difference between the common reference and the bipolar methods of derivation is that one electrode is common to all or to a group of channels. This electrode is called a common reference. In a common reference derivation, each amplifier is connected between one active electrode and the reference electrode. In common average reference derivations all the electrodes on the scalp are connected through equal resistors to a single point which is then used as a common reference. Each amplifier is connected between an active electrode and the average reference point.