Extensive cone-dependent spectral opponency within a discrete zone of the lateral geniculate nucleus supporting mouse color vision

Color vision, originating with opponent processing of spectrally distinct photoreceptor signals, plays important roles in animal behavior.(1-4) Surprisingly, however, comparatively little is understood about color processing in the brain, including in widely used laboratory mammals such as mice. The retinal gradient in Sand M-cone opsin (co-)expression has traditionally been considered an impediment to mouse color vision.(5-8) However, recent data indicate that mice exhibit robust chromatic discrimination within the central-upper visual field.(9) Retinal color opponency has been reported to emerge from superimposing inhibitory surround receptive fields on the cone opsin expression gradient, and by introducing opponent rod signals in retinal regions with sparse M-cone opsin expression.(10-13) The relative importance of these proposed mechanisms in determining the properties of neurons at higher visual processing stages remains unknown. We address these questions using multielectrode recordings from the lateral geniculate nucleus (LGN) in mice with altered M-cone spectral sensitivity (Opn1mw(R)) and multispectral stimuli that allow selective modulation of signaling by individual opsin classes. Remarkably, we find many (similar to 25%) LGN cells are color opponent, that such cells are localized to a distinct medial LGN zone and that their properties cannot simply be explained by the proposed retinal opponent mechanisms. Opponent responses in LGN can be driven solely by cones, independent of cone-opsin expression gradients and rod input, with many cells exhibiting spatially congruent antagonistic receptive fields. Our data therefore suggest previously unidentified mechanisms may support extensive and sophisticated color processing in the mouse LGN.

Automated summary

Color vision, originated from opponent processing of spectrally distinct photoreceptor signals, plays crucial roles in animal behavior, including in laboratory mammals like mice. Recent studies have found that mice demonstrate robust chromatic discrimination in the central-upper visual field, challenging the traditional notion of color vision impediment due to the expression gradient of Sand M-cone opsin in the retina. Moreover, new mechanisms beyond the proposed retinal opponent processes may be involved in supporting extensive and sophisticated color processing in the mouse lateral geniculate nucleus (LGN).