Comparison of evoked potential source localization and functioned MRI in a four-shell ellipsoidal volume conductor

A four-shell ellipsoidal model had been developed for EEG and MRI applications, using a multipole expansion in ellipsoidal coordinates. The model provides accurate distribution of potentials and surface current density generated by a dipole placed in the inner most ellipsoid. The dipole can be anywhere in any direction in the ellipsoid. Surface Laplacian data obtained from EEG measurements are fit to the surface current density from each of the models in a least squares sense for comparisons of the resulting dipole locations and orientations. The dipole location estimated from somatosensory evoked potentials is compared to the location of activation in functional MRI experiments using somatosensory stimulation.