A local Hjorth Laplacian is ideally suited for intracranial electrode grids on the dural surface, because volume conduction allows current closure not only orthogonal to the cortical surface (i.e., across laminae), but tangentially (within cortical or across columns) as well. Field closure would be evidenced by sharply localized radial sources (sinks), with smaller sinks (sources) identifiable as computational artifacts that will shift in location with changes in resolution (Tenke et al., 1993). Depending on the stimuli used and the comparisons made across conditions (e.g., random drift patterns in visual regions), this approach could help to isolate and interpret measures of local activity when local cancellation and field closure dominate the available data. Conversely, the omission of field closure as a consideration in LFP studies may contribute to findings that suggest an unexpectedly strong attenuation of field potentials over space, and that thereby challenge known properties of volume conduction (e.g., Katzner, 2009; Linden et al., 2011). Although assertions that the LFP may be restricted in scale to a few hundred microns have been countered using one-dimensional CSD methods (e.g., Kajikawa and
