Abstracts

Rationale: This study looks for differences in the waveforms of interictal epileptiform discharges (IEDs) between cortices expressing only isolated discharges (irritative zones) vs those manifesting seizures (epileptogenic zones). Identifying such differences can help to understand ictogenesis mechanisms and improve clinical decision making in surgical epilepsy.  Methods: IEDs waveforms differ across the surface of a focus, with persistent/enhanced slow-waves in the periphery. As slow-waves are known to reflect neurophysiological inhibition, peripheral slow-wave persistence may reflect surround inhibition, a mechanism characterized in experimental models, curbing seizures’ spread: in epileptogenic zones it may possibly be weakened. This study is a retrospective analysis of human intracranial EEGs, comparing IED waveforms of irritative vs epileptogenic zones, assessing for differences in peripheral slow-wave persistence. Results: Peripheral slow-wave persistence manifests in irritative zones but is weakened in epileptogenic zones. Irritative zones also exhibit persistent positive-baseline-shifts, more homogeneous spatial spread, and more frequent shifts of spread pathways. Conclusions: Peripheral slow-wave persistence correlates with inhibition of epileptiform spread corroborating the hypothesis that it may correspond to surround inhibition. Thus, waveform analysis of intracranial EEGs routinely obtained in surgical epilepsy, may help distinguishing irritative from epileptogenic zones and indicate underlying ictogenesis mechanisms. Funding: None