Retinal output changes qualitatively with every change in ambient illuminance

The collective activity pattern of retinal ganglion cells, the retinal code, underlies higher visual processing. How does the ambient illuminance of the visual scene influence this retinal output? We recorded from isolated mouse and pig retina and from mouse dLGN in-vivo at up to seven ambient light levels covering the scotopic to photopic regimes. Across each luminance transition, the majority of ganglion cells exhibited qualitative response changes, while maintaining stable responses within each luminance. Strikingly, we commonly observed the appearance and disappearance of ON responses in OFF cells and vice versa. Such qualitative response changes occurred for a variety of stimuli, including full-field and localized contrast steps, and naturalistic movies. Our results suggest that the retinal code is not fixed but varies with every change of ambient luminance. This finding raises new questions about signal processing within the retina and has intriguing implications for visual processing in higher brain areas.