None of the above considerations affect the validity of the surface Laplacian or CSD. To the contrary, they underscore the consistency of these methods, and suggest that the efficient descriptions provided by CSD-PCA may, at times, be more relevant to the generator localization problem than a precise, but model-dependent, inverse solution that leads to erroneous conclusions. Being immune to the nonuniqueness that plagues inverse models (i.e., multiple solutions using a different number of generators are equally valid), or by their assumptions about the nature and distribution of underlying neuronal generators (i.e., number and orientation of dipoles; orientation of intracranial current flow), scalp-based CSD recordings provide a conservative description of the source image at the scalp, while also imposing constraints by which the physiological plausibility of a generator may be evaluated.
