Axonal patterns and topography of short-axon neurons in visual areas 17, 18, and 19 of the cat.

In a Golgi study of short-axon cells in areas 17, 18, and 19 of the adult cat, 21 main axonal arborization patterns are distinguished and related to laminar position and dendritic morphology. Multipolar neurons exclusive to layer 2/3 exhibit the greatest diversity of axons: These may be arranged in a local tuft, a single descending stem with recurrent collaterals, a columnar descending plexus, horsetaillike bundles, a dense intralaminar plexus, or a varicose local arbor. Multipolar cells of layers 2--5 may have local basket or chandelier axons or a neurogliform axonal plexus, and axons in layer 4 may branch into a columnar basket plexus. Two types of multipolar cells are described in layers 5 and 6. Also, neurons with a bitufted dendritic tree have different axonal patterns: cone-shaped axons, arcade axons, profuse ascending plexuses, and columnar or diffuse ascending and descending arbors. The axons of bitufted cells in layer 6 ascend or form a local tuft. Finally, giant bitufted cells with local axons, bitufted or multipolar cells with horizontal axons, and bipolar cells are described. The neuronal types established on the basis of their axonal arbor are compared to previous classifications of cortical neurons. The location of neurons thus classified has been recorded and evaluated. Most cells show no topographical specificity and occur indistinctly in the three visual areas, while two types are exclusive to area 17. Horsetail neurons accumulate at the 17/18 and 18/19 borders. Multipolar cells of layer 2/3 with a dense intralaminar plexus and chandelier cells are concentrated in the region where the central visual field is represented.