The pattern of projection of cortical areas 17, 18, and 19 onto the laminae of the dorsal lateral geniculate nucleus in the cat

Abstract

The projection of cortical areas 17, 18, and 19 onto the laminar part of the dorsal lateral geniculate nucleus was investigated with degeneration methods and with the autoradiographic axon tracing method. In agreement with previous accounts, degenerating cortical axons stained by the Nauta method were restricted to laminae A, A₁, C and to the interlaminar zones. In contrast, adjacent sections stained with the Fink-Heimer method showed fine dust like degeneration throughout all of the laminae of the nucleus. Comparisons of Fink-Heimer degeneration resulting from lesions of area 17 with that resulting from lesions of areas 18 and 19 further suggested that the area 17 projection is heavier and more uniform than the projections from areas 18 and 19. Autoradiographic tracing of axons after intracortical injections of ³H-proline provided detailed demonstrations of the cortical projection patterns that confirmed the Fink-Heimer results. Following restricted injections of areas 17 or 18 the termination zones in the dorsal lateral geniculate nucleus consisted of columns of labeled tissue oriented perpendicular to the laminae of the nucleus. Area 17 was found to project heavily and uniformly throughout all of the laminae of the nucleus. The projection from area 18 also extended throughout all of the laminae of the nucleus, but was sparser and less uniformly distributed than that from area 17. Projections from area 18 distributed more heavily to the interlaminar zones and to lamina C than to laminae A, A₁, C₁, C₂, or C₃. A projection from area 19 to laminae C₁, C₂, and C₃ was also demonstrated autoradiographically.