Volume currents in forward and inverse MEG simulations using realistic head models

Many magnetoencephalography (MEG) forward and inverse simulation models employ spheres, a singular shape which does not require consideration of volume currents. With more realistic, inhomogenous, anisotropic, non-spherical head models, volume currents cannot be ignored. We verify the accuracy of the finite element methods in MEG simulations by comparing its results for a sphere containing dipoles to those obtained from the analytic solution. We then use the finite element method to show that in a realistic model, the magnetic field normal to the MEG detector due to volume currents often has a magnitude on the same order of greater than the magnitude of the primary magnetic field from the dipole. Forward and inverse MEG simulations using the realistic model demonstrate the disparity in results between calculations containing volume currents and those without volume currents. Volume currents should be included in any accurate calculation of MEG results, whether they be for a forward or inverse simulation.