S55 Epileptogenicity biomarkers and effective connectivity in stereo-EEG

Abstract

Objectives By analyzing the responses to intracranial electrical stimulation we aim at im-proving the localization of the seizure onset zone (SOZ) and the connectivity between different areas. Methods Our center uses a set of traditional and innovative advanced analysis methods for stereo-EEG signals recorded using depth electrodes. We analyze stimulation-evoked activity in time-frequency domain to detect inter-ictal epileptogenicity biomarkers like high-frequency oscillations (HFO, f > 80 Hz) and delayed responses (DR, t > 100 ms). Results of the different quantitative EEG analyses are represented as 3-D maps superimposed with patient’s anatomy, as visible on various imaging modalities, and their evolution in time is shown as movies. Cortico-cortical evoked potentials (CCEP) based on early responses (t = 10–110 ms) to single-pulse intracranial stimulation are used to calculate functional connectivity between cortical areas. Results Biomarker response maps and effective connectomes were calculated in a population of 24 patients undergoing presurgical evaluation for drug-resistant epilepsy. The sensitivity with respect to SOZ of HFOs was higher than the one of the DR by both response and stimulation location, whereas the specificity of the DRs was higher by the lo-cation of the stimulation. Discussion Despite variable sensitivity and specificity of the biomarkers, the positive pre-diction level of these biomarkers is less than 30%, taken separately or in combination. Conclusions Analysis of responses to intracranial electrical stimulation can contribute to the identification of the epileptogenic networks and for delineating the epileptogenic are-as. Significance We illustrate the value of using multiple advanced signal analysis techniques.