Interictal high-frequency oscillations in focal human epilepsy

Abstract

Purpose of review Localization of focal epileptic brain is critical for successful epilepsy surgery and focal brain stimulation. Despite significant progress, roughly half of all patients undergoing focal surgical resection, and most patients receiving focal electrical stimulation, are not seizure free. There is intense interest in high-frequency oscillations (HFOs) recorded with intracranial electroencephalography as potential biomarkers to improve epileptogenic brain localization, resective surgery, and focal electrical stimulation. The present review examines the evidence that HFOs are clinically useful biomarkers. Recent findings Performing the PubMed search ‘High-Frequency Oscillations and Epilepsy’ for 2013–2015 identifies 308 articles exploring HFO characteristics, physiological significance, and potential clinical applications. Summary There is strong evidence that HFOs are spatially associated with epileptic brain. There remain, however, significant challenges for clinical translation of HFOs as epileptogenic brain biomarkers: Differentiating true HFO from the high-frequency power changes associated with increased neuronal firing and bandpass filtering sharp transients. Distinguishing pathological HFO from normal physiological HFO. Classifying tissue under individual electrodes as normal or pathological. Sharing data and algorithms so research results can be reproduced across laboratories. Multicenter prospective trials to provide definitive evidence of clinical utility.

A method for the topographical identification and quantification of high frequency oscillations in intracranial electroencephalography recordings

“…There is strong evidence that HFOs are a biomarker of epileptogenic brain (Jacobs et al, 2008), and utilizing HFO rates for clinical applications will require accurate HFO detection (Cimbalnik et al, 2016), and an agreed upon ripple classification scheme. Quantifying HFO rates using iEEG recordings from the epilepsy monitoring unit or operating room has been proposed as a means to identify epileptogenic brain regions (van ’t Klooster et al, 2015a, 2015b) and studies have suggested that simultaneous HFOs and inter-ictal epileptiform spikes (IES) are stronger indicators of epileptogenic tissue than IES events alone (Jacobs et al, 2008).…”

Advances of Intracranial Electroencephalography in Localizing the Epileptogenic Zone

“…The rate of interictal HFOs is usually considered to be the most important parameter [26]. The rates of HFOs vary across different studies.…”

Progress and remaining challenges in the application of high frequency oscillations as biomarkers of epileptic brain

“…While early studies were focused on the frequency band of the HFOs oscillations to classify them as pathologic or physiologic, considering the wide range of overlapping pHFOs and nHFOs frequencies [3,4,11,18,42–44], more recent studies have explored other frequency-independent characteristics of HFOs: rate, amplitude, and duration [45–52]. Regions showing a high rate of interictal HFOs have been correlated with pathological epileptic tissue in different studies [2,15,48,52–54].…”

“…While there has been significant progress in automated detection of HFOs, reliably distinguishing normal physiological oscillations from pathological epileptiform oscillations [2,11,15] remains a fundamental challenge in epileptology [16–18]. …”