Frequency domain EEG source localization of ictal epileptiform activity inpatients with partial complex epilepsy of temporal lobe origin

The aim of this study was to investigate whether EEG source localization in the frequency domain, using the FFT dipole approximation (Lehmann, D. and Michel, C.M. Electroenceph. clin. Neurophysiol., 1990, 76: 271-276), would be useful for quantifying the frequency content of epileptic seizure activi ty. Between one and 7 extracranially recorded seizures were analyzed in eac h of 7 patients with mesolimbic epilepsy, who were seizure-free after tempo ral lobe resection. The full scalp frequency spectrum for the first 4 s aft er seizure onset, as well as for subsequent periods, was determined. Power peaks in the spectra were identified, and an instant dipole fit was perform ed for the frequencies corresponding to these peaks. Ictal frequencies, ran ging between 3.5 and 8.5 Hz, showed a variable degree of stability over tim e in the different patients. For a particular frequency, dipole results wer e similar during the different phases of seizure development. In patients w ith more than one prominent frequency, dipole results for the different fre quencies were similar. Dipole results were also similar between patients. W e conclude that dipole localization of dominant frequencies, as obtained fr om full scalp FFT analysis, gives quite reproducible results for seizures o riginating in the mesial temporal area. The method may become a useful tool for the pre-surgical identification of patients with mesolimbic epilepsy. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.