COLOR ENCODING OF CONTRAST IN RETINAL GANGLION CELLS REVEALED BY USING PERTURBED NATURAL IMAGES

Retinal ganglion cells(RGCs) are the output of the retinal circuit, yet how they encode color information from natural scenes remains poorly understood. In particular, it is unclear how color information contribute to contrast encoding in specific RGC populations in the mouse retina.
However, to obtain reliable activation of RGCs by green and ultraviolet(UV) light, a precise balancing ratio of M- and S-opsin isomerisations is needed. This balancing isomerisations ratio varies along the retinal ventro-dorsal axis and align with natural conditions in ventral retina (Quetu et al., 2026).
Therefore, as a first step, we first calibrated color stimuli to ensure reliable cellular responses to green and UV light. We developed a short calibration protocol to determine this isomerisation ratio at different retinal locations using multielectrode arrays. We further correlated these ratios with the local distribution of M- and S-opsins along the ventro-dorsal axis to study the relation between isomerisation ratio and M/S-opsins density ratio.
Interestingly, when using colored chirps (full-field stimuli modulated in light intensity) at this balancing isomerisation ratio, we found that RGCs respond more reliably to combined green and UV stimulation than to either color alone. Moreover, simultaneous two-color chirps elicited a stronger nonlinear responses.
Finally, we used a color perturbative stimulus approach for probing natural image processing in the retina. This approach applies a color-specific, low-contrast perturbation superimposed on naturalistic stimuli, enabling decomposition of color interactions during complex feature extraction.
Presenting stimuli at the calibrated isomerisation ratio removed the uncertainty in the color responses due to light intensity.