Simulation of the effect of conductivity changes due to tumors, ischemia and edema in the human brain on the EEG

Abstract

The impact of disorders on the EEG signal caused by tumors, ischemia or vasogenous edema has been evaluated. Hereby we offer explanations for the results of recent studies on animals and predict the effect on measurements on humans. In the grey and white matter we changed the magnitude and the anisotropy of the electrical conductivity tensors, as it is caused by expanding bleedings, ischemia or tumors. The dipole-sources, representing the neural activity in our model, were placed at different positions in gyri and sulci and aligned radially and tangentially to the surface. We solved the EEG forward problem using the finite elements method in a subvolume of a simplified model of a human head.

The simulated electric potentials on the scalp show a strong impact on the magnitude for tangential sources. An amplification of more than 600% could be observed. The effect of radial sources was considerably lower. Remarkably the signal amplitude of a radial dipole in a sulcus is higher than the signal of a gyrus when both are having an ischemic area underneath. The sulcus’ signal was amplified by 5 times and more.

Our results show that pathological changes have to be considered when evaluating EEG signals, especially when doing source localizations. Predictions cannot be made without considering the geometry, which has a strong impact on the current density distribution and can even lead to stronger signals from sources in a sulcus than from a gyrus. The effect of the magnitude change by a vasogenous edema has to be taken into account for the use of monitoring of patients at acute risk of vasogenous edema. Knowing the propagation of the electric field changed by diseases is also highly important for the technique of deep brain stimulation, which is used in the treatment of Parkinson’s disease.