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S. P. Ahlfors, G. V. Simpson. Geometrical interpretation of fMRI-guided MEG/EEG inverse estimates. NeuroImage, 22(1):323-332, 2004.


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Magneto- and electroencephalography (MEG/EEG) and functional magnetic resonance imaging (fMRI) provide complementary information about the functional organization of the human brain. An important advantage of MEG/EEG is the millisecond time resolution in detecting electrical activity in the cerebral cortex. The interpretation of MEG/EEG signals, however, is limited by the difficulty of determining the spatial distribution of the neural activity. Functional MRI can help in the MEG/EEG source analysis by suggesting likely locations of activity. We present a geometric interpretation of fMRI-guided inverse solutions in which the MEG/EEG source estimate minimizes a distance to a subspace defined by the fMRI data. In this subspace regularization (SSR) approach, the fMRI bias does not assume preferred amplitudes for MEG/EEG sources, only locations. Characteristic dependence of the source estimates on the regularization parameters is illustrated with simulations. When the fMRI locations match the true MEG/EEG source locations, they serve to bias the underdetermined MEG/EEG inverse solution toward the fMRI loci. Importantly, when the fMRI loci do not match the true MEG/EEG loci, the solution is insensitive to those fMRI loci


S. P. Ahlfors
G. V. Simpson

BibTex Reference

   Author = {Ahlfors, S. P. and Simpson, G. V.},
   Title = {Geometrical interpretation of f{MRI}-guided {MEG}/{EEG} inverse estimates},
   Journal = {NeuroImage},
   Volume = {22},
   Number = {1},
   Pages = {323--332},
   Year = {2004}

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