The dipole layer as a model for scalp potentials.

Estimates are made of the potential field at the scalp and cortical surfaces due to large numbers of synchronously active cortical current sources. The basic model is a dipole layer in an infinite, homogeneous conducting medium. Estimates are made of the effects of various inhomogeneities on the attenuation of potentials. It is shown that these approximate methods seem to illuminate the following questions which are of interest in EEG research: (1) The interpretation of reference recordings in terms of local source currents; (2) The differences in amplitude between scalp and cortical recordings; (3) The differences in frequency spectra between scalp and cortical recordings; (4) The observation that alpha rhythm can be recorded deep in the brain; and (5) The effects of simple inhomogeneities on the attenuation of potentials.