spatially enhanced representation of current generators with more sharply localized peaks than those of the scalp potential, while eliminating volume-conducted contributions from distant regions and sources (Tenke and Kayser, 2012). CSD topography thus represents reference-free estimates of radial current flow at the scalp represented in positive and negative polarities (Kayser and Tenke, 2015). The positivity or “source” represents current flow from the brain towards the scalp (i.e., outward flow), while the negativity or “sink” indicates current flow towards the brain from the scalp (i.e., inward flow) (Nunez and Srinivasan, 2006). CSD methods have been successfully implemented in several neuropsychiatric disorders (Kamarajan et al., 2015) including alcoholism (Ramachandran et al., 1996; Ji et al., 1999; Hada et al., 2000; Kamarajan et al., 2005a; Kamarajan et al., 2012) in order to understand possible brain sources underlying scalp-recorded potentials. In the present study, CSD maps were constructed from the Laplacian transformed grand averaged data of P3 amplitudes, for each group and condition, as described by Wang and Begleiter (1999). Z-scored maps for P3 amplitude as well as CSD were plotted so that topographic patterns could be compared across groups regardless of the magnitude of amplitude/CSD. Topographic activation patterns of sources and sinks between
