Influence of conductivity tensors on the scalp electrical potential: study with 2-D finite element models

The influence of conductivity tensor on the forward solution of electroencephalography was assessed in 2-D head models of a human subject. The conductivity tensors of different regions of the head were estimated from magnetic resonance-diffusion tensor images by linearly mapping the mean trace values to the published conductivity values. The anisotropic conductivity model was compared with the isotropic conductivity model in terms of the difference between the scalp potentials. The differences were measured by the cross correlation (CC) and the relative error (RE) between two models. We have also proposed a new measure, scaling-removed RE (SRRE) as a more effective indicator of the difference. The results with 354 individual dipole sources show that there are remarkable differences between the anisotropic conductivity tensor and the isotropic model (CC=0.96, RE=30.73% and SRRE=19.34%). Although the CC is high, the large RE and SRRE indicate that this difference may also affect the accuracy of inverse solutions in localizing the current dipole sources.