Frequency-based Connectivity Analysis of Interictal iEEG to Localize the Epileptogenic Focus

Resective surgery of the epileptogenic focus may be the only option for selected patients with refractory epilepsy. Accurate determination of the focus is of paramount diagnostic importance, from a better selection of surgical candidates to improvement of surgery outcome. A novel localization algorithm has been developed, based on methods of measurement of information flow and its further processing. We used the measure of Generalized Partial Directed Coherence (GPDC) for analysis of long-term interictal (between seizures) intracranial electroencephalographic (iEEG) signals from 3 patients with temporal lobe epilepsy to quantify the directional information flows between brain sites, and an outlier detection statistic to identify the brain site receiving the maximum and most frequent information inflow from the other recording sites. In two out of the three patients the clinically assessed focus was detected by the algorithm as a statistically significant (p<;0.01) outlier with respect to information inflow. In the third patient, even though not statistically significant (at significance level a=0.01), the focus still had the highest inflow value. These results indicate that estimation of brain´s connectivity from advanced analysis of iEEG may shed light on localization of the epileptogenic focus and lead to a more accurate pre-surgical evaluation of epileptic patients.