HORIZONTAL CELLS OF THE PRIMATE RETINA - CONE SPECIFICITY WITHOUT SPECTRAL OPPONENCY

The chromatic dimensions of human color vision have a neural basis in the retina. Ganglion cells, the output neurons of the retina, exhibit spectral opponency; they are excited by some wavelengths and inhibited by others. The hypothesis that the opponent circuitry emerges from se lective connections between horizontal cell interneurons and cone phot oreceptors sensitive to long, middle, and short wavelengths (L-, M-, a nd S-cones) was tested by physiologically and anatomically characteriz ing cone connections of horizontal cell mosaics in macaque monkeys. H1 horizontal cells received input only from L- and M-cones, whereas H2 horizontal cells received a strong input from S-cones and a weaker inp ut from L- and M-cones. All cone inputs were the same sign, and both h orizontal cell types lacked opponency. Despite cone type selectivity, the horizontal cell cannot be the locus of an opponent transformation in primates, including humans.