Evaluation of Errors in Estimating an Electric Dipole in the Brain

An algorithm has been constructed for estimating an electrical dipole location and its moment in the brain from the scalp potentials measured with 16 electrodes. In this case, the precise head shape is taken into account and a homogeneous conductivity is assumed. The validity of the algorithm has been investigated by animal experiments. For this purpose a pair of thin wires was inserted into the cerebrum of a cat and an impulse current was applied across them to generate a current dipole in it. Dipole locations in the brain were estimated from the scalp potentials with the aid of the boundary element method. The estimated dipole locations deviate from the real ones and the deviations are not random but rather systematic. They are displaced towards the center of the cerebrum, and the deviations are probably caused by the lack of uniformity in conductivity. The mean deviation of dipole locations in the cortex is 3 mm.