When neural activity is confined to a few regions with small extents, the fMRI analysis should yield several fMRI foci (or hotspots). It is reasonable to model the electrical activity at each fMRI hotspot as an equivalent regional current dipole. The dipole locations are fixed to the fMRI foci, or initially seeded to the fMRI foci, yet are adjustable to best fit the EEG/MEG data. Given the dipole locations are assigned or estimated, the dipole moments can be uniquely estimated by fitting the ECD model to the EEG/MEG data. From the estimated dipole time course, one can tell the temporal dynamics of the regional neural activity. Note that the primary goal of the fMRI-seeded dipole fitting technique is not to image brain activity; rather, it aims at retrieving the time course of the brain activity at identified fMRI activation foci. However, this technique is questionable when applied to imaging extended neural responses.
