The surface Laplacian, high resolution EEG and controversies.

The surface Laplacian estimate (i.e., current source density) as obtained with spline functions is evaluated in the context of some recent controversies concerning high resolution EEG and source localization. In simulation studies, the spline-Laplacian provides much better estimates of cortical surface potential than is obtained from raw scalp potential, provided dense electrode arrays (e.g., 64 or more electrodes) are used. Spline-Laplacians (which are relatively independent of volume conductor model) provide estimates of cortical potential distribution which are quite similar to those obtained with a cortical imaging algorithm based on a four sphere model.