title: Localization of cortico-peripheral coherence with electroencephalography.
abstract: BACKGROUND
  The analysis of coherent networks from continuous recordings of neural activity with functional MRI or magnetoencephalography has provided important new insights into brain physiology and pathology. Here we assess whether valid localizations of coherent cortical networks can also be obtained from high-resolution electroencephalography (EEG) recordings.
  
  
  METHODS
  EEG was recorded from healthy subjects and from patients with ischemic brain lesions during a tonic hand muscle contraction task and during continuous visual stimulation with an alternating checkerboard. These tasks induce oscillations in the primary hand motor area or in the primary visual cortex, respectively, which are coherent with extracerebral signals (hand muscle electromyogram or visual stimulation frequency). Cortical oscillations were reconstructed with different inverse solutions and the coherence between oscillations at each cortical voxel and the extracerebral signals was calculated. Moreover, simulations of coherent point sources were performed.
  
  
  RESULTS
  Cortico-muscular coherence was correctly localized to the primary hand motor area and the steady-state visual evoked potentials to the primary visual cortex in all subjects and patients. Sophisticated head models tended to yield better localization accuracy than a single sphere model. A Minimum Variance Beamformer (MVBF) provided more accurate and focal localizations of simulated point sources than an L2 Minimum Norm (MN) inverse solution. In the real datasets, the MN maps had less localization error but were less focal than MVBF maps.
  
  
  CONCLUSIONS
  EEG can localize coherent cortical networks with sufficient accuracy.
authors.affiliation: Division of Neurorehabilitation, Department of Clinical Neurosciences, University Hospital Geneva, Geneva, Switzerland. aguggis@gmail.com
authors.forename: Adrian G
authors.initials: AG
authors.lastname: Guggisberg
authors.forename: Sarang S
authors.initials: SS
authors.lastname: Dalal
authors.forename: Johanna M
authors.initials: JM
authors.lastname: Zumer
authors.forename: Daniel D
authors.initials: DD
authors.lastname: Wong
authors.forename: Sviatlana
authors.initials: S
authors.lastname: Dubovik
authors.forename: Christoph M
authors.initials: CM
authors.lastname: Michel
authors.forename: Armin
authors.initials: A
authors.lastname: Schnider
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D001931:Brain Mapping / Q000379:methods*; D002540:Cerebral Cortex / Q000502:physiology*; D003344:Cortical Synchronization / Q000502:physiology*; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D009434:Neural Pathways / Q000502:physiology*; D041623:Tomography, Optical Coherence