Pattern and field in cortical structure: The rabbit

Abstract Previous attempts at classification of cortical neurons have been based on a number of anatomical characteristics, some of doubtful physiological significance. In seeking a functionally more relevant scheme, we have based our classification on three neural attributes; (a) size and shape of the dendritic domain, (b) presence or absence of dendritic spines, and (c) intra or extra‐cortical trajectory of the axon, as revealed in Golgi stained material. Our data indicate that neurons with extra‐cortically projecting axons (long axons) invariably possess spine‐rich dendrites forming domains with remarkably regular horizontal parameters (i.e. modular domains). Cells with axons limited to intra‐cortical paths (short axons) are characterized by spine‐poor or spine‐free dendrites forming domains which are highly variable in size and shape. These two categories appear dependant on structural characteristics related both to input and output functions of cortical neurons, and are called Class I and II, respectively. The significance of synaptic arrangements along horizontal and vertical components of Class I dendritic modules are compared with those for Class II cells, and possible relationships between dendritic structure and temporo‐spatial activity patterns are considered.