The present P300 source reconstruction study used two dipoles per hemisphere in the final source space. The 4-dipole configuration was in basic agreement with previously published dipole studies (Frodl et al. 2000; Hegerl and Frodl-Bauch 1997), except for interhemispheric orientation symmetry of the dipole pairs. In fMRI studies of auditory oddball paradigm (Linden et al. 1999; Mulert et al. 2004), predominating activations of bilateral supramarginal gyri or temporoparietal regions and insula were always found, fMRI activations and EEG–LORETA current source density activations of auditory oddball also showed good correspondence in the bilateral temporoparietal region and insula (Mulert et al. 2004). Although anatomical locations of the 4-dipole model are not accurately consistent with fMRI activations, there is an approximate correspondence. Since dipole source waveforms are not much affected by errors in the center location of up to 1–2 cm (Scherg and Picton 1991; Bledowski et al. 2004), it is reasonable they reflect the brain electric activities in around bilateral temporoparietal and insula regions.
