Instrumentation for EEG and MEG

Abstract This chapter discusses all aspects of EEG and MEG hardware and instrumentation. Various electrode types for recording of EEG and other electrophysiological signals are presented and their usage and advantages and disadvantages evaluated. Principles of differential EEG amplifiers are introduced. Common-mode rejection is explained with simple examples. The influence of the reference electrode site on the potential distributions is explained in detail, together with different options for digital re-referencing. The working principles are described for superconducting quantum interference devices (SQUIDs), which are the sensors used in traditional low-temperature MEG systems. The vastly different effects of the shape of the flux transformers for the measured field patterns are illustrated. The newest developments in “room-temperature MEG” carried out with optically pumped magnetometers (OPMs) are described. The chapter ends by discussing shielding requirements for MEG installations and ways in which noise-free environments might be maintained in MEG and EEG laboratories.