title: Frequency domain beamforming of magnetoencephalographic beta band activity in epilepsy patients with focal cortical dysplasia.
abstract: BACKGROUND
  Spike-based magnetoencephalography (MEG) source localization is an established method in the presurgical evaluation of epilepsy patients. Focal cortical dysplasias (FCDs) are associated with focal epileptic discharges of variable morphologies in the beta frequency band in addition to single epileptic spikes. Therefore, we investigated the potential diagnostic value of MEG-based localization of spike-independent beta band (12-30Hz) activity generated by epileptogenic lesions.
  
  
  METHODS
  Five patients with FCD IIB underwent MEG. In one patient, invasive EEG (iEEG) was recorded simultaneously with MEG. In two patients, iEEG succeeded MEG, and two patients had MEG only. MEG and iEEG were evaluated for epileptic spikes. Two minutes of iEEG data and MEG epochs with no spikes as well as MEG epochs with epileptic spikes were analyzed in the frequency domain. MEG oscillatory beta band activity was localized using Dynamic Imaging of Coherent Sources.
  
  
  RESULTS
  Intralesional beta band activity was coherent between simultaneous MEG and iEEG recordings. Continuous 14Hz beta band power correlated with the rate of interictal epileptic discharges detected in iEEG. In cases where visual MEG evaluation revealed epileptic spikes, the sources of beta band activity localized within <2cm of the epileptogenic lesion as shown on magnetic resonance imaging. This result held even when visually marked epileptic spikes were deselected. When epileptic spikes were detectable in iEEG but not MEG, MEG beta band activity source localization failed.
  
  
  CONCLUSIONS
  Source localization of beta band activity has the potential to contribute to the identification of epileptic foci in addition to source localization of visually marked epileptic spikes. Thus, this technique may assist in the localization of epileptic foci in patients with suspected FCD.
authors.affiliation: Ruhr-Epileptology, Department of Neurology, University Hospital Knappschaftskrankenhaus Bochum, Germany; Epilepsy Center, University Medical Center Freiburg, Germany. Electronic address: marcel.heers@gmail.com.
authors.forename: Marcel
authors.initials: M
authors.lastname: Heers
authors.affiliation: Institute of Clinical Neuroscience and Medical Psychology, Heinrich Heine University Düsseldorf, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Hirschmann
authors.affiliation: Epilepsy Center, University Medical Center Freiburg, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Jacobs
authors.affiliation: Epilepsy Center, University Medical Center Freiburg, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Dümpelmann
authors.affiliation: Institute of Clinical Neuroscience and Medical Psychology, Heinrich Heine University Düsseldorf, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Butz
authors.affiliation: Department of Neurosurgery, University Hospital Bonn, Germany.
authors.forename: Marec
authors.initials: M
authors.lastname: von Lehe
authors.affiliation: Department of Epileptology, University Hospital Bonn, Germany.
authors.forename: Christian E
authors.initials: CE
authors.lastname: Elger
authors.affiliation: Institute of Clinical Neuroscience and Medical Psychology, Heinrich Heine University Düsseldorf, Germany.
authors.forename: Alfons
authors.initials: A
authors.lastname: Schnitzler
authors.affiliation: Ruhr-Epileptology, Department of Neurology, University Hospital Knappschaftskrankenhaus Bochum, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Wellmer
mesh_terms: D000328:Adult; D001611:Beta Rhythm / Q000502:physiology*; D001931:Brain Mapping; D004569:Electroencephalography; D004827:Epilepsy / Q000150:complications* / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography; D008297:Male; D054220:Malformations of Cortical Development / Q000150:complications* / Q000175:diagnosis*; D008875:Middle Aged
keywords: Dynamic Imaging of Coherent Sources (DICS); Focal cortical dysplasia (FCD); Focal epilepsy; Frequency domain beamforming; Intracranial EEG (iEEG); Magnetoencephalography (MEG)