Correlation between skull thickness asymmetry and scalp potential estimated by a numerical model of the head.

The contribution of asymmetric skull thickness to the scalp potential amplitude was investigated numerically. The model consisted of four conductive layers representing the scalp, the skull, the cerebrospinal fluid, and the cortex with a current dipole in the occipital region. The potential created by the dipole was calculated assuming quasistatic formulation and linear media. The governing equation was discretized by the finite volume method to ensure the conservation of fluxes even in regions with abrupt changes of the conductivity. The large set of the algebraic equations for the electric potential was solved iteratively by the successive overrelaxation method. The model confirmed previous experimental studies suggesting that the potential amplitude is 60% smaller on the side with the thicker bone if the asymmetry of the skull thickness exceeds 40%. The model developed suggests that skull thickness asymmetry can create nonnegligible asymmetries in the potential measured on the scalp above homotopic points of the two hemispheres.