Conductivity Estimation for EEG: What is Relevant?

The accuracy of EEG forward models partially depends on the head tissue conductivites. Some methods have been proposed to estimate these conductivities. They are all based on the idea of imposing the electrical source in the head, and considering the conductivities as the only unknowns. Although the conductivity models are becoming more and more complex, it is not clear in the literature whether it is really possible to estimate the conductivities of all the head tissues. We present here the limits of conductivity estimation for the common three-layer model (brain, skull, scalp), with and without skull anisotropy.