1. University of Washington, Dept of Biological Structure and the Washington National Primate Research Center, Seattle, Washington 98195-7420, USA
2. Departments of Neuroscience and Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2185, USA
3. University of Chicago, Vision Science Laboratories, 940 East 57 Street, Chicago, Illinois 60637, USA
4. University of Alabama at Birmingham, Vision Science Research Center, Birmingham, Alabama 35294-4390, USA

Correspondence to: Dennis M. Dacey¹ Correspondence and requests for materials should be addressed to D.M.D. (Email: dmd@u.washington.edu).

Abstract

Human vision starts with the activation of rod photoreceptors in dim light and short (S)-, medium (M)-, and long (L)- wavelength-sensitive cone photoreceptors in daylight. Recently a parallel, non-rod, non-cone photoreceptive pathway, arising from a population of retinal ganglion cells, was discovered in nocturnal rodents¹. These ganglion cells express the putative photopigment melanopsin and by signalling gross changes in light intensity serve the subconscious, 'non-image-forming' functions of circadian photoentrainment and pupil constriction^{1, 2, 3, 4, 5, 6, 7}. Here we show an anatomically distinct population of 'giant', melanopsin-expressing ganglion cells in the primate retina that, in addition to being intrinsically photosensitive, are strongly activated by rods and cones, and display a rare, S-Off, (L + M)-On type of colour-opponent receptive field. The intrinsic, rod and (L + M) cone-derived light responses combine in these giant cells to signal irradiance over the full dynamic range of human vision. In accordance with cone-based colour opponency, the giant cells project to the lateral geniculate nucleus, the thalamic relay to primary visual cortex. Thus, in the diurnal trichromatic primate, 'non-image-forming' and conventional 'image-forming' retinal pathways are merged, and the melanopsin-based signal might contribute to conscious visual perception.

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