title: Simultaneous subdural and scalp EEG correlates of frontal lobe epileptic sources.
abstract: OBJECTIVE
  To assess the visibility and detectability in scalp electroencephalography (EEG) of cortical sources in frontal lobe epilepsy (FLE) as to their localization, and the extent and amplitude of activation.
  
  
  METHODS
  We analyzed the simultaneous subdural and scalp interictal EEG recordings of 14 patients with refractory frontal lobe epilepsy (FLE) associated with focal cortical dysplasia. Subdural spike types were identified and averaged for source localization and detection of their scalp EEG correlates. Both raw and averaged scalp EEG segments were reviewed for spikes, blinded to subdural segments. We further analyzed the correlation of spike-to-background amplitude ratios in subdural and scalp EEG.
  
  
  RESULTS
  We identified 36 spike types in subdural EEG, corresponding to 29 distinct sources. Four of 29 sources were visible by visual evaluation of scalp EEG and six additional sources were detectable after averaging: four in the medial frontal, two in the dorsolateral gyri, two in the depth of dorsolateral sulci, and two in the basal frontal region. Cortical sources generating scalp-detectable spikes presented a median of 6 cm(2) of activated cortical convexity surface and a subdural spike-to-background-amplitude ratio >8. These sources were associated with a higher number of activated subdural grid contacts and a higher subdural spike-to-background amplitude ratio than sources generating non-scalp-detectable spikes.
  
  
  CONCLUSIONS
  Not only dorsolateral but also basal and medial sources can be detectable in FLE. This is the first in vivo demonstration derived from simultaneous subdural and scalp EEG recordings of the complementary significance of extensive source activation and higher subdural spike-to-background amplitude ratio in the detection of cortical sources in FLE.
authors.affiliation: Epilepsy Center, University Hospital Freiburg, Freiburg, Germany.
authors.forename: Georgia
authors.initials: G
authors.lastname: Ramantani
authors.forename: Matthias
authors.initials: M
authors.lastname: Dümpelmann
authors.forename: Laurent
authors.initials: L
authors.lastname: Koessler
authors.forename: Armin
authors.initials: A
authors.lastname: Brandt
authors.forename: Delphine
authors.initials: D
authors.lastname: Cosandier-Rimélé
authors.forename: Josef
authors.initials: J
authors.lastname: Zentner
authors.forename: Andreas
authors.initials: A
authors.lastname: Schulze-Bonhage
authors.forename: Louis Georges
authors.initials: LG
authors.lastname: Maillard
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000293:Adolescent; D000328:Adult; D004569:Electroencephalography / Q000379:methods*; D017034:Epilepsy, Frontal Lobe / Q000175:diagnosis* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012535:Scalp / Q000503:physiopathology*; D013355:Subdural Space / Q000503:physiopathology*; D055815:Young Adult
keywords: Intracranial recordings; Refractory epilepsy; Source localization