Understanding electroencephalography (EEG) and EEG instrumentation requires a basic knowledge of the recorded parameters. This chapter begins with a description of eventrelated potentials, the main EEG frequency bands, and their behavioral significance. EEG instrumentation proper is then elucidated, with a particular emphasis on biofeedback practitioners' interests and questions. (Italics on first use of a term in text indicate that the term is included in the glossary at the end of this chapter.)
The EEG results from the summation of excitatory and inhibitory postsynaptic potentials (PSPs) in the pyramidal cells of the upper layers of the cerebral cortex, with some contribution of granular and glia cell activity (for reviews, see Creutzfeldt, 1974; Lopes da Silva, 1991; Speckmann & Elger, 1999). Extracellular current flow associated with such postsynaptic activity leads to large field potentials that can be recorded on the surface of the scalp (see Figure 5.1).
The EEG rhythms are defined as regularly recurring waveforms of similar shape and duration. They are of cortical origin, but subcortical structures (particularly the thalamus) contribute to their special characteristics. The dominant EEG frequency bands are called alpha (8–13 hertz "Hz"), beta (13–30 Hz), gamma (30–100 Hz), theta (4–7 Hz), and delta (0.5–4 Hz). In addition, direct current (DC) shifts of less than 1 Hz are referred to as slow cortical potentials.
erally, the normal adult waking EEG can be classified into two main patterns. The synchronized EEG pattern measured in a relaxed, eyes-closed state is characterized by rhythmic,