These common reference schemes yield a smaller, volume-conducted N1 at midline sites, which is nevertheless considered an integral part of the basic olfactory ERP morphology (e.g., Turetsky et al., 2003a). In contrast, the ensuing olfactory P2 is not compromised by a linked-ear or -mastoid reference. It corresponds to a robust P2 source spanning mid-centroparietal regions, is accompanied by current sinks over lateral frontotemporal sites, and appears to reflect odor evaluation, as its topography resembles the P3 source associated with a classical P3b (e.g. Lorig, 2000; Olofsson et al., 2008). Taken together, this N1/P2 complex may be the olfactory equivalent of an N2/P3 complex in the auditory or visual modality, perhaps with similar functional properties (Kayser et al., 2010).
