Given that locations A-I (Fig. 7) were assumed to represent equally-spaced sites on the surface of a sphere, they may be directly used to represent known scalp locations, such as those marking the coronal plane of the 10–10 system (e.g., Jurcak et al., 2007) from the left lateral temporal (T7) through vertex (Cz) to right lateral temporal (T8). In this scenario, the ‘observed’ negative surface potential maximum at Cz, its gradual fall-off towards mid-central sites (C3/4) and steep decline towards temporal sites (T7/8) approximate a typical auditory N1 ERP topography, which has a negative maximum over mid-frontocentral sites at about 100 ms post stimulus onset (e.g., Näätänen and Picton, 1987). Figure 8A shows a complete typical auditory N1 topography for a 72-channel EEG montage (average reference) and the corresponding surface Laplacian (CSD) estimates using spherical splines of different flexibility (m = 2 .. 5). Although the ERP N1 maximum is at FCz, Cz shows the most negative value across the nine centrotemporal sites (marked as gray circles in Fig. 8A). Similarly, overall N1 minima (most positive values) are bilaterally at
