With regard to the early mid-frontal old/new effects, the observed generator pattern is reminiscent of old/new effects overlapping a prominent response-related sink (cf. Kayser et al., 2007). It strongly suggests regional dipole activity oriented orthogonally to the cortical surface within the longitudinal fissure (anterior cingulate) with opposite orientations in the two hemispheres, which results in local field closure and typically manifests as focal activity at distinct midline recording locations (the error-related negativity is a prominent example; e.g., Gehring et al., 1993). Importantly, such local field cancellations are efficiently described by CSD methods but may not be appropriately resolved by popular inverse source localization algorithms, such as LORETA or BESA (Tenke and Kayser, 2008; see also Tenke at al., 2010).
