The aforementioned concerns also illustrate frequently misunderstood properties of volume conduction in general, and the surface Laplacian in particular: 1) a surface Laplacian can detect deep generators, despite a relatively greater attenuation than field potentials (compare bottom two rows of Fig. 7G); 2) a surface Laplacian topography can provide a valuable and interpretable indication of the structure, location and orientation of intracranial generators, even though they are derived from estimates of radial scalp currents; 3) despite its nominal identification as high-resolution EEG, a Laplacian derived from a low density montage can yield group summaries and statistics that are useful, stable, and closely comparable to those derived from a high density solution (Kayser and Tenke, 2006 a,b); 4) high density measures (not only Laplacians) may themselves be subject to greater spatial noise, owing to greater relative variability in the placement of electrodes (i.e., small scale EEG gradients require greater spatial precision, but closely spaced electrodes are more prone to the spread of electrolyte, and even to electrolyte bridges between electrodes; Tenke and Kayser, 2001; Greishar et al., 2004); and 5) some open-field generator configurations may be better described using low- than high-density Laplacian estimates (Tenke et al., 1993).
