title: Identifying the epileptogenic zone in interictal resting-state MEG source-space networks.
abstract: In one third of patients, seizures remain after epilepsy surgery, meaning that improved preoperative evaluation methods are needed to identify the epileptogenic zone. A potential framework for such a method is network theory, as it can be applied to noninvasive recordings, even in the absence of epileptiform activity. Our aim was to identify the epileptogenic zone on the basis of hub status of local brain areas in interictal magnetoencephalography (MEG) networks.
  
  
  
  Preoperative eyes-closed resting-state MEG recordings were retrospectively analyzed in 22 patients with refractory epilepsy, of whom 14 were seizure-free 1 year after surgery. Beamformer-based time series were reconstructed for 90 cortical and subcortical automated anatomic labeling (AAL) regions of interest (ROIs). Broadband functional connectivity was estimated using the phase lag index in artifact-free epochs without interictal epileptiform abnormalities. A minimum spanning tree was generated to represent the network, and the hub status of each ROI was calculated using betweenness centrality, which indicates the centrality of a node in a network. The correspondence of resection cavity to hub values was evaluated on four levels: resection cavity, lobar, hemisphere, and temporal versus extratemporal areas.
  
  
  
  Hubs were localized within the resection cavity in 8 of 14 seizure-free patients and in zero of 8 patients who were not seizure-free (57% sensitivity, 100% specificity, 73% accuracy). Hubs were localized in the lobe of resection in 9 of 14 seizure-free patients and in zero of 8 patients who were not seizure-free (64% sensitivity, 100% specificity, 77% accuracy). For the other two levels, the true negatives are unknown; hence, only sensitivity could be determined: hubs coincided with both the resection hemisphere and the resection location (temporal versus extratemporal) in 11 of 14 seizure-free patients (79% sensitivity).
  
  
  
  Identifying hubs noninvasively before surgery is a valuable approach with the potential of indicating the epileptogenic zone in patients without interictal abnormalities.
authors.affiliation: Department of Clinical Neurophysiology and MEG Center, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Ida A
authors.initials: IA
authors.lastname: Nissen
authors.affiliation: Department of Clinical Neurophysiology and MEG Center, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Cornelis J
authors.initials: CJ
authors.lastname: Stam
authors.affiliation: Brain Tumor Center Amsterdam & Department of Neurology, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Jaap C
authors.initials: JC
authors.lastname: Reijneveld
authors.affiliation: Department of Clinical Neurophysiology and MEG Center, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Ilse E C W
authors.initials: IE
authors.lastname: van Straaten
authors.affiliation: Department of Radiology & Nuclear Medicine, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Eef J
authors.initials: EJ
authors.lastname: Hendriks
authors.affiliation: Neurosurgical Center Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Johannes C
authors.initials: JC
authors.lastname: Baayen
authors.affiliation: Neurosurgical Center Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Philip C
authors.initials: PC
authors.lastname: De Witt Hamer
authors.affiliation: Neurosurgical Center Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Sander
authors.initials: S
authors.lastname: Idema
authors.affiliation: Department of Clinical Neurophysiology and MEG Center, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Arjan
authors.initials: A
authors.lastname: Hillebrand
mesh_terms: D000328:Adult; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping; D000069279:Drug Resistant Epilepsy / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology* / Q000601:surgery; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography; D008297:Male; D008875:Middle Aged; D009426:Netherlands; D012372:ROC Curve; D055815:Young Adult
keywords: Beamformer-based virtual electrodes; Betweenness centrality; Epilepsy; Functional network; Hub; Neurosurgery