Abstracts

Rationale: One of the most important aspects of epilepsy surgery is localizing the epileptic networks and the seizure onset zone. While this can be straightforward in cases such as mesial temporal sclerosis, it is much more challenging in cases such as nonlesional cortical epilepsy. Animal research suggests that high frequency EEG may better localize epileptic networks than standard clinical techniques. It has therefore been suggested that all intracranial EEG (iEEG) used for seizure localization be performed beyond the clinical bandwidth of 0.1-70 Hz. Clinicians traditionally focus on the ictal onset patterns of intracranial EEG (iEEG) seizures; however several studies have shown that high frequency activity better localizes to seizure onset zones. This study intends to determine if faster EEG sampling leads to improved seizure localization when viewed in standard EEG viewing software. Methods: Fourteen seizures in ten different patients with intracranial EEG were recorded with > 2000 Hz sampling rate. Those EEGs were then filtered and downsampled to 100 Hz, 200 Hz, 500 Hz, and 1000 Hz. They were then reviewed by neurophysiologists blinded to the patient and EEG data. The reviewers reading the EEGs were able to expand the study within traditional EEG software in order to identify any high frequency activity. Results: Each physician found insignificant differences between the seizure onset time and location with the different sampling rates. Conclusions: While recent work has shown the utility of high frequency oscillations in seizure localization, translating such high bandwidth data into clinical practice will require novel strategies. It is unclear how to incorporate these findings into clinical workflow, and our results suggest that higher bandwidth EEG has only minor effects on EEG interpretation when viewed with standard EEG software. Additional tools will likely be needed to incorporate high frequency EEG into clinical practice.