Potential fields, EEG maps, and cortical spike generators.

From analysis of the interictal discharge, one can deduce the location of the underlying generator or source. Despite the geometric complications of cortical convolutions and major fissures, clinical neurophysiologists fearlessly make statements about localization of the source. In fact, this is usually nothing more than a qualitative dipole localization, which is seldom discussed with the concern of non-unique mathematical solutions. However, further information can be gleaned from the spike topography if one applies some simple constraints or assumptions (discrete point source, columnar organization). An explanation of the tangential and radial fields of centrotemporal spikes is offered, together with an attempt to rationalize why the tangential topography is associated with a more benign clinical picture than the radial topography. It is suggested that there is differential epileptogenicity between gyral and fissural cortex. Extension of this is made to multiple subpial transection.