Source Derivation assuming a spherical geometry for the head: Applications in topographic brain mapping

Source Derivation (SD) is a technique that emphasizes brain electrical activity below the electrodes. Topographic maps have been made to compare the effects of different assumptions regarding head geometry, II the spatial selectivity of SD. First, we used a local orthogonal tangential coordinate system assuming a planar surface, then a spherical head was considered and a local curvilinear coordinate system was employed. The algorithm is based on the finite difference method for non-uniform grids. With simulated and EEG data, improved source derivation in spherical geometry was found.