Identification of epileptogenic foci from causal analysis of ECoG interictal spike activity

Objective: In patients with intractable epilepsy, the use of interictal spikes as surrogate markers of the epileptogenic cortex has generated significant interest. Previous studies have suggested that the cortical generators of the interictal spikes are correlated with the epileptogenic cortex as identified from the ictal recordings. We hypothesize that causal analysis of the functional brain networks during interictal spikes are correlated with the clinically-defined epileptogenic zone. Methods: We employed a time-varying causality measure, the adaptive directed transfer function (ADTF), to identify the cortical sources of the interictal spike activity in eight patients with medically intractable neocortical-onset epilepsy. The results were then compared to the foci identified by the epileptologists. Results: In all eight patients, the majority of the ADTF-calculated source activity was observed within the clinically-defined SOZs. Furthermore, in three of the five patients with two separate epileptogenic foci, the calculated source activity was correlated with both cortical sites. Conclusions: The ADTF method identified the cortical sources of the interictal spike activity as originating from the same cortical locations as the recorded ictal activity. Significance: Evaluation of the sources of the cortical networks obtained during interictal spikes may provide information as to the generators underlying the ictal activity.