Accurate spatiotemporal retinal responses require a color intensity balance fine-tuned to natural conditions

Color vision is vital for animal survival, essential for foraging and predator detection. In mice, as in other mammals, color vision originates in the retina, where photoreceptor signals are processed by neural circuits. However, retinal responses to stimuli involving multiple colors are still not well understood. One possible explanation of this knowledge gap is that previous studies have not thoroughly examined how neuronal activity adapts to a 30 seconds to a few minutes timescale when exposed to multiple color sources. To address this, we systematically varied the UV-to-green light balance with a custom-built stimulator targeting mice opsins spectra while recording retinal ganglion cell responses in the ventral retina using multielectrode arrays. Responses to full-field chirp and checkerboard stimulations with alternating UV and green light revealed that more than one order of magnitude of intensity difference favoring green M- opsin over UV S-opsin is needed for a balanced reliability in retinal ganglion cell responses. An incorrect balance, with slightly increased UV light, silenced responses to green illumination. To determine if these values are consistent with natural conditions, we analyzed isomerisation rates in the mouse retina across different times of the day. We found that the M- to S-opsin activation ratio remains constant through the mesopic-photopic range, and our empirically determined values align well with these natural conditions, lying far from a simple equalization of M- and S-opsin isomerisation rates. In conclusion, a finely tuned color intensity balance is essential for accurately measuring both fast temporal responses and detailed spatial receptive fields.