SPATIAL ENCODING EMERGES FROM COLOUR CIRCUITS IN THE RETINA OF LARVAL ZEBRAFISH

In vertebrate vision, bipolar cells combine signals from multiple cone photoreceptor types. While this is typically linked to colour processing, cones vary in gain and spatiotemporal tuning¹ resulting in non-spectral computation². Here, we identify bipolar cells at the second synapse of vision which leverage strong colour opponency to encode asymmetric space-time features through gabor-like receptive fields, built from multiple cone channels.
Using 2P in vivo imaging and multispectral stimulation we assess bipolar cell receptive fields in larval zebrafish. Most bipolar cells show weak spatial tuning. However, a subset of cells exhibit offset, similarly weighted On- and Off-lobes under white light. We show that these offsets emerge from spatially asymmetric receptive field contributions from distinct cone types. Moreover, these offsets largely disappear under pharmacological block of amacrine cells, implicating inhibitory networks in building colour-emergent spatial representation. Preliminary results suggest receptive field asymmetries are linked to spatiotemporal encoding, which may enable orientation and direction selectivity.
Our results therefore suggest distinct spatial encoding channels can emerge from colour processing. Together, this provides new insights into how photoreceptor diversity can be leveraged in building complex non-spectral representations in early vision.

1. Baden, T., 2024. Ancestral photoreceptor diversity as the basis of visual behaviour. Nat Ecol Evol 1–13.
2. Fornetto, C., Euler, T., Baden, T., 2025. Zebrafish use spectral information to suppress the visual background. Cell 188, 7512-7528.e13.