Sensitivity Analysis of Depth EEG Electrodes to Dipolar Electric Sources

This paper presents a theoretical evaluation of the influence of the geometry and dimensions of depth EEG electrodes upon their sensitivity to equivalent current dipole sources. The electrodes we consider here are cylindrical and coaxial. Results obtained from a solution of the current density distribution for a pair of electrically stimulated electrodes are first presented. They are then used with the reciprocity theorem to assess the sensitivity of the electrodes. The potential differences between a pair of real electrodes, calculated for various positions of a dipole source, are compared to the one calculated for a pair of point electrodes of zero dimensions in the same conditions. It is shown that discrepancies of the order of 25-30 percent and 10-15 percent are, respectively, found for near and far sources between the potential differences predicted for the real electrodes and the point electrodes. These findings may be of further interest to improve models of electric potential distribution in the brain where the electrodes are considered as point electrodes.