Recent reports have suggested that field potentials recorded within the brain are in general, extremely local phenomena, reflecting neuronal processes occurring within approximately 200–400 μm of the recording electrode in the cortex (Katzner et al., 2009;Xing et al., 2009). This basic proposition is imbued in the common use of the term local field potential (LFP), which has become widespread in the literature, particularly over the last 10 years. However, the proposition seems at odds with many prior studies, which suggest that LFPs spread laterally over distances of 600~1000 μm (Berens et al., 2008), 2–3 mm (Nauhaus et al., 2009; Wang et al., 2005), 5 mm (Kreiman et al., 2006), and vertically over centimeter scales (Schroeder et al., 1992). Importantly, reports emphasizing the extreme local origins of the LFP (Katzner et al., 2009;Xing et al., 2009) have been largely confined to visual cortices on the brain surface, and have analyzed the spread of LFPs only in the “lateral” dimension. This is but one of the relevant dimensions that need to be considered, especially given that models of the underlying generators of
