It merits emphasis that, while CSD analysis can help one identify volume conduction effects beyond the margins of activated neuronal substrates, the ability of any differentiation procedure to estimate the spatial spread of the LFP is confounded in situations when separable generator substrates (e.g., cortical layers) are densely packed in the brain, and neuronal activity in a surrounding area influences the LFP at any point in the extracellular medium. Recent findings in a study employing large visual stimuli (Ray and Maunsell, 2010) might appear to argue that very limited spread of LFPs can be determined even in cases involving multiple, closely-packed generator substrates. What those findings actually show, however, is that LFPs can be differentiated over distances of ~400 μm. This is not surprising, as prior CSD studies differentiated LFPs over distances of 100 μm [e.g., (Schroeder et al., 1991)], or even 50 μm [e.g., (Mitzdorf and Singer, 1979)].
