A method for localization of sources of human cerebral potentials evoked by sensory stimuli

A method based on potential field theory is described for assessing the location and orientation of dipole generators of the human scalp-recorded sensory evoked potential (EP). The method assumes that the EP at a given moment is due to a single dipole source and that the head can be modeled by a homogeneous conductive sphere (brain) surrounded by inner (skull) and outer (scalp) shells of differing conductivity (three-sphere model). Solution for source location and orientation from the surface potential field is given for the case of a single homogeneous sphere (one-sphere model). It is then shown that a unique solution for the three-sphere model can be derived from the one-sphere solution. Solutions are obtained by application of an iterative procedure which minimizes the error between calculated and empirical potential fields. A test of the method is described in which the calculated location and orientation of a dipole was in good agreement with the known source of an early component of the human somatosensory EP.