DIPOLE ANALYSIS OF EPILEPTIC SOURCE GENERATOR WITH MANUAL ZERO POTENTIAL SHIFTING METHOD

The dipole tracing method is a technique whereby an electric source ge nerator is estimated as an equivalent current dipole (ECD) based on po tential distribution on the scalp. To estimate the electric source gen erator of low amplitude spikes, a manual zero potential shifting (MZPS ) method was introduced in which a zero potential is set manually in d ipole analysis. The subjects were three patients with localization-rel ated epilepsy with temporal spikes. When low-amplitude spikes (< 50 mu V) were analyzed by the conventional mean zero potential method, the dipolarity, an indicator of ECD reliability, had a low value and its l ocations were scattered. In contrast, when these low-amplitude spikes were analyzed by the MZPS method, ECD showed a high dipolarity value c omparable to that obtained when high-amplitude spikes (greater than or equal to 50 mu V) were analyzed by the mean zero potential method. Fu rthermore, the locations of the former ECD tended to converge and were almost identical to those of the latter ECD. These findings suggest t he usefulness of the MZPS method in dipole analysis in terms of the di polarity and ECD locations of low-amplitude spikes.