Back propagation neural network(BPNN)法によるてんかん原性焦点の推定に関する研究

Localization of the epileptogenic focus is essential in surgical treatment for intractable epilepsy. Intracranial electrical recording is now one of the accurate but invasive methods for preoperative investigation. As a possible non-invasive method for estimation of the epileptogenic focus, we have developed a topographic mapping method for two dimensional localization and the distribution of epileptic spikes (spike voltage topography : SVT). Recently, a new computer-aided method was developed to estimate the location of brain electric sources by Abeyratne et al. In this method, artificial neural network trained with a back propagation algorithm (back propagation neural network : BPNN) was used for single dipole estimation of epileptic spikes. In this paper, our clinical experiences with the BPNN method as a dipole estimation of epileptic spikes are presented and discussed. The interictal spike discharges from 11 patients (6 with partial seizures and 5 with generalized seizures) were analyzed by SVT for two dimensional localization of the epileptic spikes and the BPNN method for three dimensional localization of the dipole. The EEG of 11 patients with epilepsy was recorded from 16 channel electrodes of international 10-20 system. These data were displayed with Signal processor 7T18 for SVT, and were analyzed with the BPNN method. In five cases with partial seizure, we were able to estimate the dipole localization corresponding to the intraoperative findings with the BPNN method. On the other hand, the dipole moments of each spike showed the same direction. The dipoles of epileptic spikes in four patients of generalized seizures were estimated in the deep and central cerebral structure and the dipole moments were rotated in a clockwise or counterclockwise direction with the BPNN method. However, in another patient, the dipole existed in the left frontal region and propagated to the contralateral fronto-temporal region, and the dipole moments showed the anterio-superior direction. This finding might be implied secondary generalized seizure. Although further studies are necessary to explain the electrophysiological significance of the dipole estimation with the BPNN method, it has so far been possible to identify the three dimensional localization of epileptic spikes in most cases with partial seizure.