The influence of local tissue conductivity changes on the magnetoencephalogram and the electroencephalogram

We examined the influence of local tissue conductivity changes in the vicin ity of a dipolar source on the neuromagnetic held and the electric scalp po tential using a high resolution finite element method model of the human he ad. We found that the topology of both the electric scalp potential and the neuromagnetic field (and consequently dipole localization) is influenced s ignificantly by conductivity changes only in voxels adjacent to the source. Conductivity changes in these voxels yield a greater change in the amplitu de of the magnetic field (and consequently in the dipole strength) than in the amplitude of the electric potential.