CSD estimates are based on the second spatial derivative of the recorded surface potentials and represent the magnitude of the radial (transcranial) current flow entering (sinks) and leaving (sources) the scalp (Nunez & Srinivasan, 2006). CSD is a true reference-free technique, in that any ERP recording reference scheme will provide identical CSD estimates, which resolves the ubiquitous problem of arbitrarily choosing a reference. Moreover, by eliminating volume-conducted contributions from distant regions, CSD topographies have more sharply localized peaks than corresponding ERP topographies, and more closely represent the direction, location, and intensity of current generators that underlie an ERP topography (Mitzdorf, 1985; Nicholson, 1973). Furthermore, CSD waveforms have more focal temporal peaks than the corresponding ERP waveforms (Kayser & Tenke, 2006b), thereby providing a more precise time course of any given ERP/CSD component. Although CSD estimates are montage dependent, the surprising accuracy and reliability of low-density estimates support the comparability of high- and low-density CSD solutions, particularly for group comparisons (Kayser & Tenke, 2006c).
