Influence of Uncertainties in the Head Tissue Conductivities on the EEG Forward Problem

By James Vorwerk¹, Carsten H. Wolters², and Christopher R. Butson¹

¹Scientific Computing and Imaging (SCI) Institute, University of Utah and ²Institute for Biomagnetism and Biosignalanalysis, University of Münster

For accurate EEG [electroencepahlography] source analysis, it is necessary to solve the forward problem of EEG as exact as possible. We investigate the influence of the uncertainty with regard to the conductivity values of the different conductive compartments of the human head on the EEG forward and inverse problem. The goal is to identify for which of these compartments varying conductivity values have the strongest influence, so that these conductivity values can be individually calibrated in future studies. For the investigated source in the somatosensory cortex, the skull conductivity clearly has the strongest influence, while white and gray matter conductivities have a very low influence. If possible, an individual calibration of the skull conductivity should therefore be performed. The feasibility of a calibration of further conductivity values based on SEPs [somatosensory evoked potentials] is questionable given the dominance of the skull conductivity. This study shows that besides the geometrical modeling of the conductive compartments of the human head, also the conductivity values assumed for these compartments have a strong influence in EEG source localization.

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