It was recently observed that the local field potential (LFP) correlates with the BOLD signal (Leopold et al., 2003; Logothetis et al., 2001). Since the LFP is the basis for scalp EEG, a non-invasive method for multimodal integration could be achieved by investigating correlations between BOLD and EEG responses (Horovitz et al., 2002; Benar et al., 2007). Our approach provided additional information with respect to previous EEG–fMRI studies based on fMRI-constrained source localization of ERPs (Moores et al., 2003; Mulert et al., 2004), or on direct ERP/fMRI integration (Calhoun et al., 2006), and complemented the results of classical fMRI statistical analyses (Linden et al., 1999). These showed a large number of P300 generators, specifically in the supplementary motor area, the anterior cingulate, the middle and superior frontal cortex, the insula, the posterior parietal cortex, and the right temporo-parietal junction, which were suggested to belong to different functional systems (Bledowski et al., 2004a; Horn et al., 2003).
