Neuromagnetic source localization of auditory evoked fields and intracerebral evoked potentials: a comparison of data in the same patients

Objective: To compare the localizations of different neural sources (a) obt ained from intracerebral evoked responses and (b) calculated from surface a uditory evoked field responses recorded in the same subjects. Our aim was t o evaluate the resolving power of a source localization method currently us ed in our laboratory, which is based on a recent spatio-temporal algorithm used in magneto-encephalography (MEG). Methods: Auditory evoked responses were studied in 4 patients with medicall y intractable epilepsy. These responses were recorded from depth electrodes implanted in the auditory cortex for pre-surgical evaluation (stereo-elect ro-encephalography (SEEG)). as well as from surface captors (for MEG) place d on the scalp after removal of the depth electrodes. Auditory stimuli were clicks and short tone bursts with different frequencies. Results: All middle-latency components (from 13 to 70 ms post-stimulus onse t) were recorded and localized (via SEEG) along Heschl's gyrus (HG). MEG re liably localized Pam and Plm in the same area of HG that intracerebral reco rdings localized them in. No significant delay between SEEG and MEG latenci es was observed. Both methods suggest that N1 is generated from different s ources in the intermediate and lateral parts of the HG and in the planum te mporale (PT). The source of P2 (PT and/or Area 22) remains unclear and was in one case, localized in different regions according to the method used. T his latter component may therefore also be generated by different sources. Conclusions: The results suggest that both techniques are useful and may be used together in a complementary fashion. Intracerebral recordings allow t he researcher to validate and interpret surface recordings. (C) 2001 Elsevi er Science Ireland Ltd. All rights reserved.