Effects of head shape on EEGs and MEGs

Results are presented of computer modeling studies of the effects of head shape on electroencephalograms (EEGs) and magnetoencephalograms (MEGs) and on the localization of electrical sources in the brain using these measurements. The effects of general, nonspherical head shape are determined by comparisons of EEG and MEG maps from nonspherical head models with corresponding maps from a spherical head model. The effects on source localization accuracy are determined by calculating moving dipole inverse solutions in a spherical head model using EEGs and MEGs from the nonspherical models and comparing the solutions with those for known sources. It was found that nonspherical head shape can produce significant changes in the maps produced by some sources in the cortical region of the brain but produce localization errors of less than approximately 1 cm. No significant differences in the effects of such deviations on EEGs and MEGs were found.