TY - JOUR T1 - Circuit mechanisms underlying chromatic encoding in <em>Drosophila</em> photoreceptors JF - bioRxiv DO - 10.1101/790295 SP - 790295 AU - Sarah L. Heath AU - Matthias P. Christenson AU - Elie Oriol AU - Maia Saavedra-Weisenhaus AU - Jessica R. Kohn AU - Rudy Behnia Y1 - 2019/01/01 UR - http://biorxiv.org/content/early/2019/10/04/790295.abstract N2 - Spectral information is commonly processed in the brain through generation of antagonistic responses to different wavelengths. In many species, these color opponent signals arise as early as photoreceptor terminals. Here, we measure the spectral tuning of photoreceptors in Drosophila. In addition to a previously described pathway comparing wavelengths at each point in space, we find a horizontal-cell-mediated pathway similar to that found in mammals. This pathway enables additional spectral comparisons through lateral inhibition, expanding the range of chromatic encoding in the fly. Together, these two pathways enable optimal decorrelation of photoreceptor signals. A biologically constrained model accounts for our findings and predicts a spatio-chromatic receptive field for fly photoreceptor outputs, with a color opponent center and broadband surround. This dual mechanism combines motifs of both an insect-specific visual circuit and an evolutionarily convergent circuit architecture, endowing flies with the unique ability to extract chromatic information at distinct spatial resolutions. ER -