Regional resolving power of combined MEG/EEG

Different modeling frameworks (such as error analyses for dipole localization [Fuchs, 1998] [Huizenga, 2001]; crosstalk and point spread analyses for linear estimators [Liu, 2002]; etc.) have demonstrated improved three-dimensional (3D) resolution for combined MEG/EEG (or EMEG) source estimation. Complementary to these, an empirical analysis of 2D surface data suggested that MEG and EEG information content could be superadditive [Pflieger, 2000]. Taking a hybrid approach in the present study, we made simulations within a regional activity estimation (REGAE, [Pflieger, 2001]) framework, which quantifies the ability of EMEG to discriminate brain activity originating within a 3D region of interest (ROI) from simultaneous non-ROI activity. Two metrics were employed: Kullback-Leibler divergence (KLD) and area under the receiver operator characteristic curve (AUROC). High-density sensor configurations (248 magnetometers, 256 electrodes) were combined with a gray matter source space model (7931 dipole triples, maximum entropy activities), assuming magnetic 3-shell sphere and electric BEM head models. Superadditive KLD was observed frequently across 89 representative brain ROIs and 3 ROI sizes (5, 10, and 15 mm radii), especially for regions already fairly visible to each modality. We also report an observed functional relationship between AUROC and KLD.