To the best of our knowledge, no complete ERP waveform topography for olfactory stimuli has yet been published, except for selected midline “topographies” (Fz, Cz, Pz), probably because of concerns about individual specificity (Lorig, 2000). By overlaying individual ERPs and CSDs, we established that the grand means accurately summarized temporal and spatial properties of the observed OERP components. Figure 1 compares the grand mean olfactory ERP and CSD component structure for all 67 participants at all 31 scalp locations (averaged across intensities). 3 The OERP waveforms (solid gray lines) showed a typical negative–positive component sequence, including an N1 potential (approximate peak latency 300 ms) believed to reflect initial sensory processing of olfactory stimuli followed by a P2 potential (600 ms), which is comparable to those reported in prior studies (Pause et al., 1996; Turetsky et al., 2003). By explicitly including the mastoid reference sites (TP9/10), however, it becomes obvious that recording sites along the reference-dependent isopotential line (e.g., T7/8, FT9/10, P9/10) showed little or no ERP activity. Thus, ERP activity at these sites is severely attenuated because of the arbitrary
