Symmetric BEM formulation for the M/EEG forward problem.

The forward M/EEG problem consists in simulating the electric potential and the magnetic field produced outside the head by currents in the brain related to neural activity. All previously proposed solutions using the Boundary Element Method (BEM) were based on a double-layer integral formulation. We have developed an alternative symmetric BEM formulation, achieving a significantly higher accuracy for sources close to tissue interfaces, namely in the cortex. Numerical experiments using a spherical semi-realistic multilayer head model with a known analytical solution are presented, showing that the new BEM performs better than the formulations used in our earlier comparisons, and in most cases outperforms the Finite Element Method (FEM) as far as accuracy is concerned, thus making the BEM a viable choice.