Comparison of Single-Channel and Multichannel Magnetoencephalogram Recordings

The neuronal intracellular currents which produce magnetic fields (Okada 1989; Wikswo et al. 1981) can be detected outside the head by a sensitive magnetometer, the SQUID (super conducting quantum interference device) (Zimmerman et al. 1970). The record of the spontaneous or evoked magnetic fields is called the magnetoencephalogram (MEG) and of the electric recording, the electroencephalogram (EEG). The main difference between EEG and MEG is that the magnetic field of the MEG – in contrast to the EEG – is almost never influenced by the different conductivities of different tissues, such as brain, cerebrospinal fluid, or bone (Peters and de Munck 1990); thus the MEG has advantages over the EEG.