Cross-Frequency Coupling Features Of Postictal Generalized Eeg Suppression State

In patients with epilepsy, convulsive seizures are often followed by a postictal generalized EEC suppression (PCES) state characterized by reduced background activity. Recent studies found a correlation between seizure termination state and PCES duration, and suggested that PCES is the result of the cessation of neuronal activity. To test that assertion, we investigated ten seizure records obtained from intracranial EEC (iEEG) from six patients, four of which had Engel Class 1 surgical outcome. In each case expert neurologists identified the most likely seizure onset electrode. We found the iEEG equivalent of PCES and an artifact-free preictal quiescent state of the same window size. Using index of cross-frequency coupling (I-CFC) we identified the degree of coupling and dominant frequency bands involved in PCES and preictal quiescent states, and quantified the areas of high I-CFC. We found that there was an increase in the degree of coupling between the 0.5-1.5Hz with high gamma frequency bands in the PCES states. We found that among all of the patients, as well as in Engel Class 1 patients specifically, the change in the quantified area of high I-CFC was significant (p < 0.05) between PCES and preictal quiescent states. Furthermore, we were able to identify whether a recording was from a depth or subdural electrode, or whether it was from seizure onset zone or not using I-CFC markers in PGES. This suggests that there are frequency coupling markers that successfully identify PGES and that there are underlying dynamics that occur in this seemingly quiet postictal state.