Chunk #16 — 3. Impact of spatial scale on CSD implementations — 3.1. Empirical considerations for linear (one-dimensional) intracranial recordings — 3.1.1. The cortical dipole and field closure
The notation of a “cortical dipole” arose to explain observed surface-to-depth EEG polarity inversions in neocortex based on its well-known histological properties. Lorente de No (1947) proposed that the asymmetry and local alignment of projection cells in various regions (i.e., not simply cortical laminae, but various nuclei as well) can result in a pattern of activation that produce an “open field,” which can volume conduct over distance. In contrast, radially-symmetric or disorganized cellular alignments result in local cancellation of the potential field, identifying it as a “closed field.” The concept of field closure may be generalized to refer to those properties of a neuronal generator that result in cancellation, sculpting, or spatial distortion of a field potential between local and macroscopic scales. These properties are a direct result of the geometry (pattern) of the generator that, in turn, reflects both the cytoarchitecture and the gross anatomy of the active tissue.
