The Effect of High-frequency Cortical Stimulation on SEEG-recorded Interictal Epileptiform Discharges
Abstract
More than 15 million patients with epilepsy suffer from drug-resistant epilepsy (DRE). In these cases, a successful surgical outcome entails the removal of the seizure onset zone (SOZ), the brain region(s) responsible for seizure initiation. In this regard, finding robust biomarkers of epileptogenicity will help clinicians to accurately localize the SOZ. In focal epilepsies, interictal epileptiform discharges (IEDs) are paroxysmal events observed in both epileptogenic and non-epileptogenic zones.
To identify the SOZ, extraoperative cortical stimulation (CS) is used during phase II of the presurgical investigation. We evaluated the impact of CS on IEDs to find biomarkers of epileptogenicity to accurately find SOZ.
In this study, intracranial signals were recorded from thirty DRE patients (seizure-free post-surgery) implanted with depth electrodes (stereo-electroencephalography) for presurgical evaluation. Bipolar and high frequency (50 Hz) CS was performed with a pulse width of 300 µs and current spanning 1–6 mA. Following preprocessing, IEDs were automatically detected pre- and post-stimulation, and their normalized absolute changes were compared between SOZ and non-SOZ.
Our findings reveal a significant increase in IED numbers following CS over SOZ compared to non-SOZ stimulation (Mann-Whitney U test, p< 0.001). Furthermore, this increase extended beyond the stimulated site, indicating a broader effect of stimulation on the SOZ. These results feature the potential of tracking post-stimulation changes in IEDs’ characteristics as a quantitative method for SOZ identification, enhancing localizing the SOZ with greater precision.