Interlaminar connections of the visual cortex in the hedgehog (Paraechinus hypomelas)

The contribution of each cortical lamina to intracortical circuitry was studied in the visual neocortex of the Pakistani hedgehog. Punctate laminar lesions were made electrolytically within the visual cortex, and after five to seven days the brains were processed and stained with the Fink-Heimer technique. The results of this study suggest that both horizontal and vertical connections are important to the organization of visual cortex in the hedgehog. The horizontal projections originate at three distinct cortical depths. Lesions in layer II reveal projections that traverse the inner one-half of layer I; lesions in layers III and IV reveal projections that traverse layer IV and that enter the cortical white matter; lesions in layers V and VI reveal projections that traverse the outer one-half of layer VI and that enter the cortical white matter. The vertical projections are oriented perpendicular to the pial surface. Layers II and III project to underlying layer V. Layers V and VI in turn contribute to a reciprocal projection back to all superficial cortical laminae. This anatomical data about intracortical circuitry is discussed with reference to the functional organization of visual cortex.