Influence of Tissue Conductivity Anisotropy on EEG/MEG Field and Return Current Computation in a Realistic Finite Element Head Model

To achieve a deeper understanding of the brain, scientists and clinicians use Electroencephalography (EEG) and Magnetoencephalography (MEG) inverse methods to reconstruct sources in the cortex sheet of the human brain. There exists a persistent uncertainty regarding the influence of volume conduction effects such as the anisotropy of tissue conductivity of the skull and the white matter compartments on EEG and MEG source reconstruction.

In my talk, I will study the sensitivity to anisotropy of the EEG/MEG forward problem for deep and eccentric sources with differing orientation components in a high resolution Finite Element volume conductor. The influence of anisotropy will be presented by both high resolution visualization of field distribution, isopotential-surfaces and return current flow and topography and magnitude error measures. The combination of simulation and visualization provides a deep insight into the effect of head tissue conductivity anisotropy.

We found that for EEG, the presence of tissue anisotropy both for the skull and white matter compartment substantially compromises the forward potential computation and therefore the inverse source reconstruction. Skull anisotropy has a smearing effect on the forward potential computation. In contrast, for the MEG, only the anisotropy of the white matter compartment has an effect. The deeper the source and the more it is surrounded by anisotropic fiber bundles, the larger the effect is. Furthermore, the degree of error resulting from the uncompensated presence of tissue anisotropy depended strongly on the proximity of the anisotropy to the source, remote anisotropy had a much weaker influence than anisotropic tissue that included the source.