Effects of local skull inhomogeneities on EEG source estimation

The accuracy of the head model affects the solutions of the EEG inverse pro blems. If a simple three-sphere model and standard conductivity values for brain, skull and scalp regions are used, significant errors may occur in th e dipole localisation. One of the most sensitive head model parameters is t he conductivity of the skull. A realistic three-dimensional finite-element model provides a method to study the effect of inhomogeneities of the skull on the solutions of EEG inverse problems. In this paper the effect of a lo cal skull conductivity inhomogeneity on sourer estimation accuracy is analy zed by computer simulations for different numbers of electrodes. It is show n that if the inhomogeneity of the skull conductivity is not taken into acc ount, localisation errors of approximately 1 cm can be encountered in the e quivalent current dipole estimation. This modelling error introduces a bias to the solution which cannot be compensated by increasing the number of el ectrodes. (C) 1999 IPEM. Published by Elsevier Science Ltd. All rights rese rved.