Dien, Spencer, and Donchin (2003) used a dipole inverse model to support the anterior cingulate cortex (ACC) as a generator of novelty P3. An ACC solution has since been replicated (Debener, Makeig, Delorme, & Engel, 2005), even when the location of the dipole inverse solution has been constrained based on fMRI (Crottaz-Herbette & Menon, 2006). However, ERP and fMRI measures differ considerably both in their temporal and spatial resolution and in their biophysical substrates, suggesting that this convergence is quite fortuitous. Moreover, as previously argued (Kayser & Tenke, 2006b; Tenke & Kayser, 2005), cortical generators should be characterized by local current flow approximately normal to the cortical surface (i.e., aligned with projection cells; Klee & Rall, 1977; Lorente de No, 1947; Tenke, Schroeder, Arezzo, & Vaughan, 1993). What at first glance appears to be a parsimonious convergence of findings across methodologies actually introduces an electrophysiological paradox: Unless the generator is restricted to the banks of the cingulate sulcus, rather than the cingulate gyrus itself, the equivalent dipole should be tangential to the midline scalp. In this regard, it is notable
