Mapping of the CSD is often used to identify the neuronal generator patterns contributing to scalp-recorded EEG by providing a global empirical and biophysical context for generator localization (Tenke and Kayser, 2012). CSD transformations are implemented by algorithms that compute estimates of the current projected radially towards the skull and scalp from the underlying neuronal tissue at a given surface location, from a spatially weighted sum of the potential gradients directed at this site from some or all recording sites (cf. Kayser and Tenke, 2006b). In essence, the CSD maps represent the magnitude of the radial (transcranial) current flow from the brain to the scalp (source) and to the brain from the scalp (sink) (Perrin et al., 1989a; Kayser et al., 2012). In the CSD-converted scalp potentials, source and sink may correspond to the positive and negative (going) activity respectively. For instance, positive-going CSD activity related to a P3 potential is termed as P3 source while the negative-going CSD activity to an N1 component is described as N1 sink (Kayser et al., 2006). In effect, the CSD transformation functions as
