On generalized notions of the Epileptogenic Zone

Abstract

Objectives Contemporary interpretations of the Epileptogenic Zone (EZ) are rooted in static attributions of pathological properties to brain tissue, resulting in complex interpretations of the dynamic discharge properties. We wish to critically consider alternative EZ interpretations based on traveling discharge patterns. Methods Most commonly observed patterns in intracranial electroencephalography (iEEG) recordings comprise fast oscillations (8–30 Hz) with gradually increasing amplitude. The activity of the folded sheet is observed through the local field potential recorded on the contacts of a depth electrode. We hypothesize that the gradual amplitude increase on the recorded signals is caused by the physical translation of the neural field and the subsequent spatial averaging of the source activity. We use The Virtual Brain platform to simulate the spread of the epileptic seizure on a piece of a cortical surface located in the vicinity of the intracranial electrode of interest. Results Simulated iEEG signals exhibit the typical feature of the seizure onset pattern – slowly increasing amplitude of the oscillations. The comparison of the recorded and simulated signals in terms of the timing of the apparent seizure onset and the duration of the period of amplitude increase show also quantitative consistency, demonstrating the plausibility of the mechanism on the realistic spatial and temporal scales. Conclusion We show that that field effects of traveling neural activity along the folded cortex may mimic onset patterns at distant iEEG electrodes, in particular those with increasing oscillatory amplitude. Notably, these effects can be observed in contacts distant from the true EZ, and under certain conditions even in absence of highly epileptogenic tissue. These results underscore the importance of the computational modeling in clinical neuroscience and suggest more dynamic interpretations of the concept of Epileptogenic Zone.