Midline ERP generators have been inferred for phenomena spanning a range of cognitive and spectral paradigms (e.g., ERN/theta: Luu, Tucker, & Makeig, 2004; EEG/theta: Gevins & Smith 2000; McEvoy, Pellouchoud, Smith, & Gevins, 2001; Pizzagalli et al., 2001; but see Tenke & Kayser, 2005). There may even be a fundamental link between midline theta and novelty P3 (Demiralp, Ademoglu, Comerchero, & Polich, 2001; Isler, Grieve, Czernochowski, Starkm, & Friedman, 2008). Relevant for all these findings is that a single pair of bilaterally symmetric, midline dipoles (e.g., ACC simulation) produces sufficient field closure to impede inverse solutions (Tenke & Kayser, 2008). However, the same simulated generator produces a scalp-CSD topography that correctly describes deep sinks projecting bilaterally from the midline over the lateral frontal lobe, with uncanceled sources aligned narrowly along the overlying frontal midline (e.g., Kayser & Tenke, 2006b; Tenke & Kayser, 2005, 2008). This precise CSD pattern has also been observed in word recognition memory tasks, revealing old–new effects for a response-locked midfrontal sink with significant effects corresponding to this topography (Kayser et al., 2007). It follows, therefore, that CSD-PCA provides a comprehensive, yet conservative, linear approach for identifying and quantifying the generator patterns underlying the scalp-recorded ERP.
