Model-based EEG and MEG Source Reconstruction Methods

Neurophysiological activity, as measured with EEG or MEG, has its origin in the brain. For most EEG and MEG experiments it is known beforehand, that the folded gray matter of the cortex is the location of the neurons whose activity is measured. These neurons, the pyramidal cells, are oriented perpendicular to the cortical surface. Triangulation of the segmented cortical surface yields a triangle net holding all anatomical information which is necessary to guide the reconstruction procedure. We have developed dedicated 3D region-growing, surface subsampling, normal estimation, and surface triangulation algorithms for generating the cortical triangle net. Especially, triangle nets encode neighborhood information of the potential source locations. Neighborhood information provides additional source constraints that model the correlation of neuronal activation which is necessary to generate detectable fields or potentials at all. In a surface-based 3D visualization environment, reconstruction results are displayed as color-coded overlays together with the cortical surface, the measurement setup, and arbitrary MR data slices. The algorithms described are part of the source reconstruction software package CURRY.