High-frequency oscillations and other electrophysiological biomarkers of epilepsy: clinical studies

Greg Worrell, Jean Gotman
2011 Biomarkers in Medicine  
Accurate localization of epileptogenic brain is critical for successful epilepsy surgery. Recent research using wide bandwidth intracranial EEG has demonstrated that interictal high-frequency oscillations are preferentially localized to the brain region generating spontaneous seizures, and are a potential biomarker of epileptogenic brain. The existence of an interictal, electrophysiological biomarker of epileptogenic brain has the potential to significantly advance epilepsy surgery by improving
more » ... outcomes through improved localization and potentially eliminating the reliance on chronic intracranial EEG monitoring. Keywords epilepsy surgery; epileptogenic zone; fast ripple; high-frequency oscillation; ripple; seizure onset zone; wide bandwidth EEG Neuronal oscillations recorded from human brain span a wide range of spatiotemporal scales that extend well beyond traditional clinical EEG [1,2]. Extracellular local field potentials (LFPs) recorded from human brain range from direct current shifts to high-frequency oscillations (HFOs; ~0-1000 Hz). The mechanisms underlying these activities are varied [1], making the direct association of LFP characteristics (e.g., frequency, amplitude, spectral pattern, waveform morphology) with physiology or pathology difficult. Despite this challenge, neurophysiologists have had significant success associating physiological function and pathology with EEG activity [1]. Historically, neurophysiologists largely focused on activity in the Berger bands (1-25 Hz) [3] . Recent studies, however, report that γ-frequency oscillations and synchrony (γ: 25-80 Hz) are involved in cognitive function and pathology (for a recent review see [4, 5] ). Beyond the γ-frequency range, hippocampal ripple frequency oscillations (ripple: 80-200 Hz) are believed to be important for memory [6] [7] [8] . Ictal EEG is a powerful tool for diagnosis and classification of seizures and epilepsy. It was recognized early on that epileptogenic brain capable of generating spontaneous seizures also generated interictal epileptiform spikes and sharp waves [9] . These interictal EEG signatures of epileptogenic brain are generated by the paroxysmal discharge of large neuronal populations and are highly specific for epilepsy [10] . In addition to interictal epileptiform
doi:10.2217/bmm.11.74 pmid:22003904 pmcid:PMC3254091 fatcat:7hbt6iddzzen5dggsjqt4wnt7q