title: Sensitivity of MEG and EEG to source orientation.
abstract: An important difference between magnetoencephalography (MEG) and electroencephalography (EEG) is that MEG is insensitive to radially oriented sources. We quantified computationally the dependency of MEG and EEG on the source orientation using a forward model with realistic tissue boundaries. Similar to the simpler case of a spherical head model, in which MEG cannot see radial sources at all, for most cortical locations there was a source orientation to which MEG was insensitive. The median value for the ratio of the signal magnitude for the source orientation of the lowest and the highest sensitivity was 0.06 for MEG and 0.63 for EEG. The difference in the sensitivity to the source orientation is expected to contribute to systematic differences in the signal-to-noise ratio between MEG and EEG.
authors.affiliation: MGH/HST Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital/Harvard Medical School, 149 13th Street, Rm 2301, Charlestown, MA 02129, USA. seppo@nmr.mgh.harvard.edu
authors.forename: Seppo P
authors.initials: SP
authors.lastname: Ahlfors
authors.forename: Jooman
authors.initials: J
authors.lastname: Han
authors.forename: John W
authors.initials: JW
authors.lastname: Belliveau
authors.forename: Matti S
authors.initials: MS
authors.lastname: Hämäläinen
mesh_terms: D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology*; D004569:Electroencephalography; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008959:Models, Neurological; D009949:Orientation; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted