SYSTEMATIC COMPARISONS OF INTERPOLATION TECHNIQUES IN TOPOGRAPHIC BRAIN MAPPING

The performance of one local interpolation technique, the nearest neig hbors, and two global spline techniques, one planar and the other sphe rical, commonly used for topographic mapping of brain potential data h as been quantitatively evaluated. The method of evaluation was one of cross-validation where the potential at each site in a 31-electrode fu ll scalp recording montage is predicted by interpolation from the othe r sites. Errors between the measured potentials and those predicted by interpolation were quantified using 4 measures defined as inaccuracy, precision, bias and tolerance. The evaluation was applied to the back ground EEGs from 5 normal volunteers and from 4 patients with epilepsy , tumor or stroke. The results indicate that none of the interpolation techniques performed well and that for localized components in the EE G, the errors can increase almost without limit. Further, the global t echniques performed significantly better than the local technique with 2 being the best order for the nearest-neighbor technique and 3 for t he spline techniques. It is concluded that interpolation should not be used with electrode densities of the order of that provided by the in ternational 10-20 system neither to increase the spatial resolution of the electroencephalogram nor in more sophisticated analysis technique s in quantitative EEG for estimates such as the radial-current density .