Abstracts

Rationale: The method of current source localization provides information for identifying the generators of particular EEG activities. Pathophysiological mechanisms may also be deduced from the results of current source localization using a spatiotemporal dipole model. Using current dipole source analysis, we tried to reveal the locations and orientations of the current dipole sources for the anterior temporal spikes.Methods: We examined the scalp EEGs of 18 epileptic patients who had anterior temporal spikes on the scalp EEGs. EEGs had been recorded for at least 30 min in each patient, using a 32-channel digital EEG machine and 21 electrodes placed on the scalp according to the international 10-20 system. The sampling rate was 200 or 400 Hz. The digital EEG data were collected from 21 channels of average reference montage. Semiology of all the patients showed complex partial seizures of temporal lobe type. Ten of them had secondary generalized tonic-clonic seizures. Thirteen had no structural lesion in brain MRI and/or CT. The other 5 patients had unilateral hippocampal sclerosis in brain MRI. According to each electrode showing highest amplitude of spikes (T1, T2, F7, F8), 5, 9, 1 and 3 patients were enrolled respectively. The patients included 11 females and 7 males, with a mean age of 32.2 ± 14.5 years. An averaged spike of 15-20 spikes was obtained in each EEG. We applied a spatiotemporal dipole model to determine the locations and orientations of current dipole sources of the averaged waves.Results: The amplitude of spikes was 139.89 ± 68.52 uV (mean ± SD) and the duration of spikes was 96.72 ± 18.68 msec (mean ± SD). The dipole sources of averaged spikes were explained by 2 dipoles in 10 of the 18 patients and by a single dipole in the remaining 8 patients. The common locations were the inferior frontal gyrus, the claustrum and the insula in the cases of single or primary dipoles. In the cases of additional dipoles, the common locations were the superior frontal gyrus and the claustrum. When simplified the locations of the dipoles as the frontal, the temporal, the insular and the subcortical area, the number of cases were 8 of 18 (44.5%), 1 of 18 (5.6%), 3 of 18 (16.7%) and 6 of 18 (33.3%) respectively in the cases of single or primary dipoles. In the cases of additional dipoles, those were 3 of 8 (37.5%), 2 of 8 (25.0%), 0 of 8 (0.0%) and 3 of 8 (37.5%) respectively. The orientations of the dipole sources were radial, oblique or tangential to the temporal convexity, and horizontal, intermediate or vertical to the vertex. The most common orientation of the main dipoles was radial to the temporal convexity and intermediate to the vertex. Conclusions: The pathophysiological dipole sources in the broad area including the frontal lobe, the temporal lobe, the insula and the subcortical area may have crucial roles to generate the anterior temporal spikes on scalp EEG. The current dipole sources may frequently located in the frontal areas including the inferior frontal and the superior frontal gyrus. They may commonly have the orientation radial to the temporal convexity and intermediate to the vertex.