Influence of tissue conductivity changes on the EEG signal in the human brain: a simulation study.

Tissue disorders due to brain pathologies, like tumors, ischemia, or vasogenic edema, are known to impact the propagation of electrical fields. By using the finite element method the EEG forward problem was solved within an adapted subspace of a simplified human head model. Simulated electric potentials on the scalp revealed strong influences on the magnitude of the signal in almost all cases, even for ischemic tissue in which conductivity is lower than in healthy tissue. Remarkably, due to the "shunting effect" and the diminishing anisotropy of tissue conductivity, the signal amplitude of a radial dipole located in a sulcus was found to be higher than the signal of a dipolar source on a gyrus if the ischemic area was located underneath. The results demonstrate that pathological tissue changes have to be taken into account when evaluating EEG signals, especially when performing source localization.