TOPOGRAPHICAL RELIABILITY OF MESIO-TEMPORAL SOURCES OF INTERICTAL SPIKES IN TEMPORAL-LOBE EPILEPSY

Purpose: Localization of hippocampal paroxysmal activities in temporal lobe epilepsy (TLE) by means of dipole modeling has often been critic ized because of the supposed inaccuracy of this technique in localizin g deep sources of EEG signals. This study aimed at assessing the relev ance of mesio-temporal dipoles, as identified by modeling of scalp rec orded spikes in TLE. Methods: Surface and depth EEG activities were si multaneously recorded using scalp and intracranial electrodes implante d through the foramen ovale (FO) in 3 patients with refractory TLE sei zures. Intracranial FO spikes were used as triggers for scalp EEG aver aging. The averaged signals were modeled by current dipoles, the local ization of which were fused with patients' 3D-MRI. Results: Individual FO spikes were undetectable on visual analysis of raw scalp EEG but w ere reflected by low-amplitude scalp EEG transients on averaged signal . Dipole modeling of this EEG deflection consistently identified a mes io-limbic source in a position close to that of the FO pole recording the intracranial spike with its maximal amplitude. Conclusion: This re sult suggests that mesio-temporal sources can be accurately localized by modeling the signals recorded on the scalp, thus validating the ana tomical and clinical relevance of hippocampal sources identified by mo deling scalp interictal averaged spikes in TLE. (C) 1998 Elsevier Scie nce ireland Ltd. All rights reserved.