Synchronization clusters of interictal activity in the lateral temporal cortex of epileptic patients: Intraoperative electrocorticographic analysis

Objective: Drug-resistant temporal lobe epilepsy (TLE) can be treated by tailored surgery guided by electrocorticography (ECoG). Although its value is still controversial, ECoG activity can provide continuous information on intracortical interactions that may be useful to understand the pathophysiology of TLE. The goal of this study is to characterize local interactions in multichannel ECoG recordings of the lateral cortex of TLE patients using three synchronization measures and to link this information with surgical outcome. Methods: Intraoperative ECoG recordings from 29 TLE patients were obtained using grids of 20 electrodes (4 x 5) covering regions T1, T2, and T3 of the lateral temporal lobe. Linear correlation, mutual information, and phase synchronization were calculated to quantify lateral intracortical interactions. Surrogate data files were generated to test results statistically. Results: By distributing locally the interactions between the electrodes, we characterized the spatial patterns of ECoG activity. We found clusters of synchronized activity at specific areas of the lateral temporal cortex in most patients. Methodologically, linear correlation and phase synchronization performed better than mutual information for cluster discrimination. ROC analysis suggested that surgical removal of sharply defined synchronization clusters correlated with seizure control. Conclusions: Our results show that synchronous intraoperative ECoG activity emerges from specific cortical areas that are highly differentiated from the rest of the temporal cortex. This suggests that synchronization analysis could be used to functionally map into the temporal cortex of TLE patients. Moreover, our results suggest that these sites might be involved in the circuits that participate in clinical seizures.