Spike voltage topography and equivalent dipole localization in complex partial epilepsy

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Abstract
Summary 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.