Chunk #53 — 3. Impact of spatial scale on CSD implementations — 3.3. Empirical considerations for planar (two-dimensional) scalp-recorded EEG — 3.3.2. CSD as a conservative description of neural current generators
Alternative approaches to the inverse problem assume that neuronal tissue is continuous over sufficient distances and may therefore not be suited to a single dipole solution. One such model, termed low resolution brain electromagnetic tomography (LORETA; Pascual-Marqui et al., 1994), requires the alignment (i.e., low-resolution smoothing) of current density contributions (vector J in Eq. 2) through contiguous brain regions. From an idealized tomographic map of the gray matter, putative generators are inferred by the localization of high current densities. However, LORETA also does not restrict the direction of current flow, so that the inferred vectors fields have no relationship to the orientation of neurons and laminae within the region.8 These properties impart both strengths and limitations to the approach that complement or counter those of dipole inverse models. For these reasons, it is incorrect to assert that activity in a given region is “measured” by that model, even though it may be appropriate to refer to results as being consistent with activity in an anatomical region based on a particular inverse model. This is not a trivial distinction, because such
