title: Are high frequency oscillations associated with altered network topology in partial epilepsy?
abstract: Neurophysiological studies have reported functional network alterations in epilepsy, most consistently in the theta frequency band. Highly interconnected brain regions (so-called 'hubs') seem to be important in these epileptic networks. High frequency oscillations (HFOs) in intracranial EEG recordings are recently discovered biomarkers that can identify the epileptogenic area and are thought to result from altered neuronal interactions. We studied whether the epileptogenic zone (identified by HFOs and seizure onset zone) is associated with pathological hubs. Bilateral depth electrode recordings from the hippocampus and amygdala were available from twelve patients suspected of temporal lobe epilepsy. HFOs, classified as ripples (80-250 Hz) and fast ripples (250-500 Hz), and epileptiform spikes were marked for all patients in a five-minute epoch of slow-wave sleep. For each channel, we computed hub-measures from a period without epileptiform spikes and found that the epileptogenic zone was associated with a decreased hub-value in the theta frequency band. The amount of HFOs, especially fast ripples, was negatively correlated with the hub-value per channel. Results from post-hoc analyses of other frequency bands, particularly the broad- and gamma frequency band, pointed in the same direction as the results for the theta frequency band. These findings suggest a pathological functional 'isolation' of the epileptogenic zone in the interictal state.
authors.affiliation: Rudolf Magnus Institute of Neuroscience, Department of Pediatric Neurology, University Medical Center Utrecht, the Netherlands. E.vanDiessen-3@umcutrecht.nl
authors.forename: Eric
authors.initials: E
authors.lastname: van Diessen
authors.forename: Judith I
authors.initials: JI
authors.lastname: Hanemaaijer
authors.forename: Willem M
authors.initials: WM
authors.lastname: Otte
authors.forename: Rina
authors.initials: R
authors.lastname: Zelmann
authors.forename: Julia
authors.initials: J
authors.lastname: Jacobs
authors.forename: Floor E
authors.initials: FE
authors.lastname: Jansen
authors.forename: François
authors.initials: F
authors.lastname: Dubeau
authors.forename: Cornelis J
authors.initials: CJ
authors.lastname: Stam
authors.forename: Jean
authors.initials: J
authors.lastname: Gotman
authors.forename: Maeike
authors.initials: M
authors.lastname: Zijlmans
mesh_terms: D000328:Adult; D001921:Brain / Q000503:physiopathology*; D004567:Electrodes, Implanted; D004569:Electroencephalography; D004833:Epilepsy, Temporal Lobe / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009415:Nerve Net / Q000503:physiopathology*; D012640:Seizures / Q000503:physiopathology; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult
keywords: Functional connectivity; Graph theory; High frequency oscillations; Network analysis; Temporal lobe epilepsy