Abstracts

In most Epilepsy Surgery Centers that still utilizes ECoG during temporal lobe epilepsy (TLE) surgeries, the analysis are limited to incidence and amplitude of spikes. The study of propagation patterns to detect where spikes peak earlier (leading spikes) and to establish relationships between them (latencies) are rarely addressed. Detection of leading spikes (LS) can potentially better guide the resections and influence seizure outcome. This study addresses the correlations between basal and lateral spikes during ECoG of mesial TLE patients, searching for propagation patterns and LS. We analyzed ECoG of 20 patients (8 males, 12 females, 21 to 59 years, median 39.3 years) with mesial TLE associated to unilateral hippocampal sclerosis (HS). The selection for surgery was based on multidisciplinary protocol including high-resolution MRI, V[iacute]deo-EEG monitoring, neuropsychological, psychiatric and quality of life assessments. Pre-resection recordings were performed through subdural strips over the superior, middle and inferior temporal gyri, and strips under the temporal lobe directed towards the entorhinal c[oacute]rtex. Each recording lasted 10 minutes, at sampling rate of 1,000 Hz, and band-pass filtering of 0.3 [ndash] 300 Hz. ECoG were visually analyzed and interpeak latencies observed in 200 ms samples, exclusively between electrodes located more than 1 cm apart, in order to avoid volume conduction. LS were defined as spikes with earlier peaking, and principal leading spikes (PLE) as the ones that peaked earlier in the majority of the samples. Seven patients had right and 13 left HS. The following ECoG patterns were observed: 1) restricted basal spikes: 6/20 (30%) of patients; 2) mesial to lateral spread: 3/20 (15 %) of patients; 3) restrocted neocortical spikes: 10/20 (50%) of patients; 4) lateral to mesial spread: 1/20 (5%) of patients. Multiple LSs were found in all patients. LSs were equally located in the basal in 10/20 (50%), and in the neocortex in 10/20 (50%) of the patients, over the superior (5/20), middle (2/20) and inferior temporal gyrus (3/20 patients). Our data suggest that even homogeneous focal epilepsy syndromes can have electrophysiological heterogeneity and different patterns of spikes propagation on ECoG. There were multiples LS in half of the patients, and restricted spikes to basal temporal structures in only few patients. Despite the limitations of subdural recordings these observations suggest that even in this focal epilepsies epileptogenicity within the temporal lobe can be multifocal. (Supported by FAPESP, CNPq)