The passive transmission of electric fields through biological tissue from an underlying electrical current generator is known as volume conduction. Although volume conduction follows Maxwell’s equations, for the case of the low-frequency activity characteristic of the EEG (i.e., below 1 kHz) in a conductive medium, it can be efficiently simplified by neglecting the capacitive component of tissue impedance, as well as induction and the related electromagnetic propagation (Plonsey, 1982). The result is a linear (or piecewise-linear) relationship that parallels Ohm’s Law (V = IR), which expresses the well-known proportionality between the potential difference (voltage; V) across a conductor with a given resistance (R) in an electrical circuit and the current (I) that flows through it.
