A comparison between Y-cells in A-laminae and lamina C of cat dorsal lateral geniculate nucleus

Extracellular responses of Y-cells in the A-laminae and in lamina C of the cat dorsal lateral geniculate nucleus were recorded and compared for several sine-wave grating presentations. Both spatial and temporal contrast sensitivity functions were determined for these cells as well as suprathreshold response functions at 0.2 and 0.4 contrast. Qualitatively, the responses of the lamina C Y-cells were very similar to Y-cells of the A-laminae; differences were of a quantitative nature. At threshold, lamina C Y-cells were more sensitive at all spatial and temporal frequencies tested. Suprathreshold results showed no major differences in fundamental response amplitude between laminar Y-cells. Interlaminar differences were found with respect to second harmonic response amplitude. Lamina C Y-cells gave the largest overall second harmonic response for all stimulus conditions. A trend was observed for these laminar Y-cells such that the second harmonic responses were highest for Y-cells of lamina C, intermediate for lamina A Y-cells, and lowest for those of lamina A1. Based on differences in projection pattern and present electrophysiological results, we conclude that the lamina C Y-cells may represent a population of cells that is distinct from A-laminae Y-cells. These lamina C Y-cells provide a significant input to visual cortex.