The influence of conductivity changes in boundary element compartments on the forward and inverse problem in electroencephalography and magnetoencephalography
J. Haueisen et al., The influence of conductivity changes in boundary element compartments on the forward and inverse problem in electroencephalography and magnetoencephalography, BIOMED TECH, 44(6), 1999, pp. 150-157
Source localization based on magnetoencephalographic and electroencephalogr
aphic data requires knowledge of the conductivity values of the head. The a
im of this paper is to examine the influence of compartment conductivity ch
anges on the neuromagnetic field and the electric scalp potential for the w
idely used three compartment boundary element models. Both the analysis of
measurement data and the simulations with dipoles distributed in the brain
produced two significant results. First, we found the electric potentials t
o be approximately one order of magnitude more sensitive to conductivity ch
anges than the magnetic fields. This was valid for the field and potential
topology (and hence dipole localization), and for the amplitude (and hence
dipole strength). Second, changes in brain compartment conductivity yield t
he lowest change in the electric potentials topology (and hence dipole loca
lization), but a very strong change in the amplitude (and hence in the dipo
le strength). We conclude that for the magnetic fields the influence of com
partment conductivity changes is not important in terms of dipole localizat
ion and strength estimation. For the electric potentials however, both dipo
le localization and strength estimation are significantly influenced by the
compartment conductivity.