electromagnetism - Difference between electric and magnetic field (relating to EEG & MEG)

I study cognitive neuroscience and I periodically run into physics related questions in the context of neuroimaging technologies.

My question specifically refers to electric and magnetic fields that can be measured by electroencephalography (EEG) and Magnetoencephalography (MEG), respectively.

One interesting difference between the EEG and MEG signal is that unlike the electric field, the magnetic field is unimpeded by differing conductances across brain, skull, scalp and other tissues. I was wondering if somebody could explain what differences between the two fields account for these phenomena.