PT  - JOURNAL ARTICLE
AU  - Sarah L. Heath
AU  - Matthias P. Christenson
AU  - Elie Oriol
AU  - Maia Saavedra-Weisenhaus
AU  - Jessica R. Kohn
AU  - Rudy Behnia
TI  - Circuit mechanisms underlying chromatic encoding in <em>Drosophila</em> photoreceptors
AID  - 10.1101/790295
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 790295
4099  - http://biorxiv.org/content/early/2019/10/04/790295.short
4100  - http://biorxiv.org/content/early/2019/10/04/790295.full
AB  - 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.