Spike voltage topography and equivalent dipole localization in complex partial epilepsy.

The EEG of 45 patients with complex partial epilepsy was recorded from standard and supplementary inferior temporal electrode sites for 2 or more days via cable telemetry onto video (VHS) tape (22-25 channels, common reference). Epochs with "temporal spikes" were read into a topographic EEG device where individual spikes were visually identified and averaged in sums of 8-32. Analysis of spike voltage topography revealed two distinct patterns - dipolar, Type 1 and non-dipolar, Type 2. One or the other spike type predominated in all but two patients. Application of source modeling techniques (3 shells, single dipole, 6 parameters) to the spike topography data revealed that both spike types had similar equivalent dipoles in terms of location and orientation, except for vector elevation. However, calculated dipoles for Type 1 spikes were more stable over the course of the spike peak. Correlations with clinical data and intracranial EEG suggest that Type 1 spikes originate in mesial temporal structures, while Type 2 spikes arise from temporal or frontal neocortex. Spike voltage topography and equivalent dipole localization appear to be useful in the presurgical evaluation of patients with focal epilepsy.