Of Cats And Men: Origins of Primate Color Vision Pathways

Abstract

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 blue- ON 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 blue- ON 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.