Late High-Frequency Oscillations Evoked by Single-Pulse Electrical Stimulation Improve Mapping of the Epileptogenic Zone and Seizure Propagation Network
ObjectiveDelayed responses to single-pulse electrical stimulation are used during stereo-EEG to localise epileptogenic zone for epilepsy surgery with limited sensitivity. We investigated whether late high-frequency oscillations constitute a previously unrecognised component of the delayed-response spectrum and whether their inclusion improves identification of EZ and seizure propagation networks.MethodsWe analysed Single Pulse Electrical Stimulation responses from 799 contacts across 10 patients. Late responses >300ms post-stimulation were identified with or without accompanying late High Frequency Oscillations (80–500 Hz), and evaluated as epileptogenic zone markers. Distant Late Responses were mapped as markers of seizure propagation network.ResultsLate Responses featured Late High Frequency Oscillations in 49.1% of Late Responses. Including late High Frequency Oscillations improved localisation of epileptogenic zone (Positive Predictive Value 76.0%, Negative Predictive Value 70.3%; McNemar test p=0.046). Distant Late Responses mapped seizure propagation networks with high negative predictive value (92.7%). In a single case, radiofrequency thermocoagulation abolished all local Late Responses, whilst Early Responses remained.ConclusionsLate High Frequency Oscillations form part of a unified spectrum of delayed Single Pulse Electrical Stimulation responses, supporting shared mechanisms of pathological hypersynchrony and the use of late Single Pulse Electrical Stimulation responses as dynamic markers of epileptogenic networks.SignificanceLate HFOs may be considered part of the spectrum of Late Responses which indicate the Epileptogenic Zone.