ELECTRIC SOURCE LOCALIZATION OF THE AUDITORY P300 AGREES WITH MAGNETIC SOURCE LOCALIZATION

The event-related cortical potential elicited in the context of audito ry target detection tasks includes the N1, P2 and P3 components. The a im of the present study was to identify the sources of these scalp-rec orded components using an electrical multiple dipole model. Nine healt hy adults volunteered for the study. An auditory oddball paradigm was used. Stimuli (18% target and 82% non-target tones) were delivered thr ough ear-phones and subjects were required to silently count the targe ts. Event-related potentials (ERPs) to these stimuli were recorded by 30 electrodes placed on the scalp. The identification of the sources o f the ERP was attempted using the brain electric source analysis (BESA ) program. The instantaneous source locations of N1, P2 and P3 reporte d in magnetoencephalographic (MEG) literature were used as initial sta rting locations for the spatio-temporal multiple dipole modeling of th e EEG data. First the auditory long latency responses were modeled sep arately. Bilateral superior temporal plane sources with almost vertica l orientations explained the first 250 msec window of the non-target t one recording including N1/P2 complex. This agrees with MEG source loc alization of N1m/P2m. Two slightly deeper dipoles in superior temporal gyri and bilateral dipoles in hippocampi or parahippocampal areas exp lained P3 (analysis window 250-600 msec). The final model explained th e complete epoch of 600 msec with 6 dipoles and the residual variances of individual models ranged from 3.83% to 7.77%. The concordance betw een MEG and BESA source localization results supports the notion of ge nerators in temporal lobes for the N1/P2 complex and generators in tem poral and hippocampal areas for the P3 component.