A THEORETICAL AND EXPERIMENTAL-STUDY OF HIGH-RESOLUTION EEG BASED ON SURFACE LAPLACIANS AND CORTICAL IMAGING

Two different methods to improve the spatial resolution of EEG are dis cussed: the surface Laplacian (e.g., current source density) and corti cal imaging (e.g., spatial deconvolution). The former methods tend to be independent of head volume conductor model, whereas the latter meth ods are more model-dependent. Computer simulations of scalp potentials due to either a few isolated sources or 4200 distributed cortical sou rces and studies of actual EEG data both indicate that the two methods provide similar estimates of cortical potential distribution. Typical correlation coefficients between either spline-laplacian or cortical image and simulated (calculated) cortical potential are in the 0.8-0.9 5 range, depending partly on CSF thickness. By contrast, correlation c oefficients between simulated scalp and cortical potential are in the 0.4-0.5 range, suggesting that high resolution methods provide much be tter estimates of cortical potential than is obtained with conventiona l EEG. The two methods are aid applied to steady-state visually evoked potentials and spontaneous EEG. Correlation coefficients obtained fro m real EEG data are in the same general ranges as correlations obtaine d from simulations. The new high resolution methods can provide a dram atic increase in the information content of EEG and appear to have wid espread application in both clinical and cognitive studies.