title: Language lateralization represented by spatiotemporal mapping of magnetoencephalography.
abstract: OBJECTIVE
  Determination of hemispheric language dominance is critical for planning epilepsy surgery. We assess the usefulness of spatiotemporal source analysis of magnetoencephalography for determining language laterality.
  
  
  METHODS
  Thirty-five patients with epilepsy were studied. The patients performed a semantic word-processing task during MEG recording. Epochs containing language-related neuromagnetic activity were averaged after preprocessing. The averaged data between 250 and 550 ms after stimulus were analyzed by using dynamic statistical parametric mapping. ROIs were obtained in the opercular and triangular parts of the inferior frontal gyrus, superior temporal gyrus, and supramarginal gyrus in both hemispheres. We calculated laterality indices according to 1) dSPM-amplitude method, based on the amplitude of activation in the ROIs, and 2) dSPM-counting method, based on the number of unit dipoles with activation over a threshold in the ROIs. The threshold was determined as half of the maximum value in all ROIs for each patient. A LI ≥0.10 or ≤-0.10 was considered left- or right-hemisphere dominance, respectively; a LI between -0.10 and 0.10 was considered bilateral. All patients underwent an intracarotid amobarbital procedure as part of presurgical evaluation.
  
  
  RESULTS
  The dSPM-counting method demonstrated laterality consistent with the IAP in 32 of 35 patients (91.4%), the remaining 3 (8.6%) demonstrated bilateral language representation, whereas the dSPM-amplitude method showed 18 (51.4%) concordant and 17 (48.6%) bilateral. No laterality opposite to the IAP was found.
  
  
  CONCLUSIONS
  Spatiotemporal mapping of language lateralization with the dSPM-counting method may reduce the necessity for an IAP in as many as 90% of patients.
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA. naoro@nmr.mgh.harvard.edu
authors.forename: N
authors.initials: N
authors.lastname: Tanaka
authors.forename: H
authors.initials: H
authors.lastname: Liu
authors.forename: C
authors.initials: C
authors.lastname: Reinsberger
authors.forename: J R
authors.initials: JR
authors.lastname: Madsen
authors.forename: B F
authors.initials: BF
authors.lastname: Bourgeois
authors.forename: B A
authors.initials: BA
authors.lastname: Dworetzky
authors.forename: M S
authors.initials: MS
authors.lastname: Hämäläinen
authors.forename: S M
authors.initials: SM
authors.lastname: Stufflebeam
mesh_terms: D000293:Adolescent; D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D002540:Cerebral Cortex / Q000503:physiopathology*; D004827:Epilepsy / Q000503:physiopathology*; D005260:Female; D007839:Functional Laterality; D006801:Humans; D007802:Language; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009415:Nerve Net / Q000503:physiopathology*; D062211:Spatio-Temporal Analysis; D055815:Young Adult