Effect of forward model errors on eeg source localization.

Content Provider	CiteSeerX
Author	Acar, Zeynep Akalin Makeig, Scott
Abstract	Subject-specific four-layer boundary element method (BEM) electrical forward head models for four participants, generated from magnetic resonance (MR) head images using NFT (sccn.ucsd.edu/wiki/NFT), were used to simulate electroencephalographic (EEG) scalp potentials at 256 recorded electrode positions produced by single current dipoles of a 3-D grid in brain space. Locations of these dipoles were then estimated using gradient descent within five template head models fit to the electrode positions. These were: a spherical model, three-layer and four-layer boundary element method (BEM) head models based on the Montreal Neurological Institute (MNI) template head image, and these BEM models warped to the recorded electrode positions. Smallest localization errors (4.1 mm to 6.2 mm, medians) were obtained using the electrode-position warped four-layer BEM models, with largest localization errors ( ≈ 20 mm) for most basal brain locations. When we increased the brain-to-skull conductivity ratio assumed in the template model scalp projections from the simulated value (25:1) to a higher value (80:1) used in earlier studies, the estimated dipole locations moved outwards (12.4 mm, median). We also investigated the effects of errors in co-registering the electrode positions, of reducing electrode counts, and of adding a fifth, isotropic white matter layer to one individual head model. Results show that when individual subject MR head images are not available to construct subject-specific head models, accurate EEG source localization should employ a four- or five-layer BEM template head model incorporating an accurate skull conductivity estimate and warped to 64 or more accurately 3-D measured and co-registered electrode positions. Key words:
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Subject Keyword	Eeg Source Localization Forward Model Error Electrode Position Localization Error Head Image Recorded Electrode Position Head Model Dipole Location Subject-specific Four-layer Boundary Element Method Accurate Skull Conductivity Estimate Individual Subject Mr Head Image Scalp Potential Brain-to-skull Conductivity Ratio Four-layer Boundary Element Method Edu Wiki Nft Single Current Dipole 3-d Grid Basal Brain Location Magnetic Resonance Individual Head Model Subject-specific Head Model Five-layer Bem Template Head Model Bem Model Brain Space Co-registered Electrode Position Template Head Model Template Model Scalp Projection Electrode Count Spherical Model Montreal Neurological Institute Gradient Descent Four-layer Bem Model Accurate Eeg Source Localization Isotropic White Matter Layer
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