Effect of the skull on scalp potentials

The skull has low conductivity, which influences especially electroencephalographic (EEG) signals recorded on the scalp, but also the magneto-encephalogram (MEG). Thus the information obtained from these signals can be prominently enhanced, if the effects of the skull can be taken into account. We have used both theoretical and experimental approaches to study these effects on EEG. Our experimental results suggest that the signal transmission from the cortex to the scalp has quite low frequency dependence. The results of theoretical modelling suggest that the overall variation of the skull parameters has a relatively small effect compared to the spatial variations.