It is generally unfeasible to compute a true, three-dimensional CSD because the extensive penetration would certainly compromise the integrity of the neuronal elements underlying it, rendering the exercise futile. The theoretical limitation of the standard one-dimensional CSD is the assumption that current flows only in the dimension sampled (i.e., across laminae), but not orthogonal to it. This implies that the CSD is invariant within region, making it a suitable approach for the study of generators that are distributed across a region or cytoarchitectonic field, and consistent with an intuitive view of the cortical dipole. However, the CSD will be variable or inconsistent for penetrations through small gyri, near regional boundaries, or for oblique penetrations through highly localized fields (e.g., confined to one or a few columns), because volume conduction through a conductive medium is not directional, and there is no reason to assume that field closure is limited to a single dimension.6
