title: Negative BOLD in default-mode structures measured with EEG-MREG is larger in temporal than extra-temporal epileptic spikes.
abstract: BACKGROUND
  EEG-fMRI detects BOLD changes associated with epileptic interictal discharges (IED) and can identify epileptogenic networks in epilepsy patients. Besides positive BOLD changes, negative BOLD changes have sometimes been observed in the default-mode network, particularly using group analysis. A new fast fMRI sequence called MREG (Magnetic Resonance Encephalography) shows increased sensitivity to detect IED-related BOLD changes compared to the conventional EPI sequence, including frequent occurrence of negative BOLD responses in the DMN. The present study quantifies the concordance between the DMN and negative BOLD related to IEDs of temporal and extra-temporal origin.
  
  
  METHODS
  Focal epilepsy patients underwent simultaneous EEG-MREG. Areas of overlap were calculated between DMN regions, defined as precuneus, posterior cingulate, bilateral inferior parietal and mesial prefrontal cortices according to a standardized atlas, and significant negative BOLD changes revealed by an event-related analysis based on the timings of IED seen on EEG. Correlation between IED number/lobe of origin and the overlap were calculated.
  
  
  RESULTS
  15 patients were analyzed, some showing IED over more than one location resulting in 30 different IED types. The average overlap between negative BOLD and DMN was significantly larger in temporal (23.7 ± 19.6 cm(3)) than extra-temporal IEDs (7.4 ± 5.1 cm(3), p = 0.008). There was no significant correlation between the number of IEDs and the overlap between DMN structures and negative BOLD areas.
  
  
  CONCLUSIONS
  MREG results in an increased sensitivity to detect negative BOLD responses related to focal IED in single patients, with responses often occurring in DMN regions. In patients with high overlap with the DMN, this suggests that epileptic IEDs may be associated with a brief decrease in attention and cognitive ability. Interestingly this observation was not dependent on the frequency of IED but more common in IED of temporal origin.
authors.affiliation: Department of Neuropediatrics and Muscular Diseases, University Medical Center Freiburg Freiburg, Germany ; Epilepsy Center, University Medical Center Freiburg Freiburg, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Jacobs
authors.affiliation: Department of Neuropediatrics and Muscular Diseases, University Medical Center Freiburg Freiburg, Germany.
authors.forename: Antonia
authors.initials: A
authors.lastname: Menzel
authors.affiliation: Epilepsy Center, University Medical Center Freiburg Freiburg, Germany.
authors.forename: Georgia
authors.initials: G
authors.lastname: Ramantani
authors.affiliation: Department of Neuropediatrics and Muscular Diseases, University Medical Center Freiburg Freiburg, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Körbl
authors.affiliation: Medical Physics Freiburg, Germany.
authors.forename: Jakob
authors.initials: J
authors.lastname: Assländer
authors.affiliation: Epilepsy Center, University Medical Center Freiburg Freiburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schulze-Bonhage
authors.affiliation: Medical Physics Freiburg, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hennig
authors.affiliation: Medical Physics Freiburg, Germany.
authors.forename: Pierre
authors.initials: P
authors.lastname: LeVan
keywords: EEG-fMRI; default mode; epileptic spikes; fast fMRI; refractory epilepsy