CSD, also known as the scalp surface Laplacian, provides a representation of current generators underlying an ERP topography, which reflects the magnitude of radial current flow entering (source) and leaving (sink) the scalp (e.g., Nunez & Srinivasan, 2006). CSD analysis is a reference-free technique because any EEG recording reference scheme will yield the same, unique CSD transform for a given EEG montage. A CSD transform yields sharper topographies compared to those of scalp potentials, and also reduces redundant contributions due to volume conduction (e.g., see review by Tenke & Kayser, 2012), which also enhances the temporal resolution of the component structure. CSD waveform topographies faithfully summarize and simplify the putative generators of a scalp potential topography, and therefore represent a common bridge between scalp-recorded EEG and the underlying neuronal generators (Tenke & Kayser, 2012). The entire set of CSD waveforms can then be submitted to temporal PCA to identify relevant, data-driven components in the form of unique, orthogonal variance factors associated with generator patterns underlying stimulus processing, and thereby provide a concise and unbiased summary of the observed ERP/CSD activity (e.g., Kayser & Tenke, 2003, 2005, 2006a, Kayser et al., 2007).
