Basic Physics and Physiology of MEG and EEG

Abstract The chapter gives a general overview of the basic physics and physiology of MEG and EEG signals. The relationship between electric charges and electric currents is described, as well as some basic laws that relate current to voltage, resistance, and conductivity. Next, the relationship between currents and magnetic fields is examined, followed by introduction of superconductivity and its relevance to MEG. This leads into a discussion of source currents in the brain and how they can be identified by solving the so-called inverse problem. It is shown that the shape and conductivity of the volume conductor—comprising different tissues of the head—affect MEG and EEG differently, as relating to the detectability of currents in the brain. General points about volume conduction and cancellation of activity are also stressed. The chapter ends by touching on the spatial and temporal resolution and precision of MEG and EEG.