Of Cats And Men: Origins of Primate Color Vision Pathways

Most non primate mammals are known to possess dichromatic color vision based on short-wavelength-sensitive (S) and medium/long-wavelength-sensitive (ML) cone photoreceptors. However, the neural pathways carrying signals underlying the primitive “blue–yellow” axis of color vision are largely unexplored in these animals. We have recently characterized a population of color opponent blueON cells in electrophysiological single-cell recordings from the dorsal lateral geniculate nucleus (LGN) of anaesthetized cats. We found remarkable similarities to previous descriptions of primate blue-ON cells in terms of receptive field size and structure and the relative weight of functional inputs from the opponent cone classes. Moreover, cat blueON cells were found in the same layers as W-cells, which are thought to be homologous to the primate koniocellular system. The temporal frequency optimum of cat blue-ON cells was around 3 Hz, about one-third of that found in achromatic cells. Based on these data, we suggest that cat blue-ON cells are part of a "blue-yellow" color opponent system that is the evolutionary homologue of the blue-ON division of the koniocellular pathway in primates.