Numerical tests of a method for simulating electrical potentials on the cortical surface

The cortical imaging technique (CIT) based on solving a harmonic inward continuation problem is validated by applying it to artificially derived data. Pairs of dipolar sources with different depths and separations are introduced into a spherical conducting medium simulating the head. Scalp potential maps are constructed by interpolating the simulated data between 28 scalp electrode positions. Noise is added to the data to approximate the variability in measured potentials that would be observed in practice. CIT is used in each case to construct potential maps on layers concentric to and within the layer representing the scalp. In several instances when the dipole pair is deep and closely spaced, the sources cannot be separated by the scalp topographical maps but are easily separated by the cortical topographical maps. CIT is also applied to scalp-recorded potentials evoked by bilateral median nerve stimulation and pattern-reversal visual stimulation. Applications of CIT to scalp-recorded potentials suggest that it might be possible to draw inferences about the neural generators of these potentials.