Spectral inference reveals principal cone-integration rules of the zebrafish inner retina

In the vertebrate retina, bipolar cells integrate the signals from different cone types at two main sites: directly, via dendritic inputs in the outer retina, and indirectly, via axonal inputs in the inner retina. Of these, the functional wiring of the indirect route, involving diverse amacrine cell circuits, remains largely uncharted. However, because cone-photoreceptor types differ in their spectral sensitivities, insights into the total functional cone-integration logic of bipolar cell might be gained by linking spectral responses across these two populations of neurons. To explore the feasibility of such a “spectral-circuit-mapping” approach, we here recorded in vivo responses of bipolar cell presynaptic terminals in larval zebrafish to widefield but spectrally resolved flashes of light. We then mapped the results onto the previously established spectral sensitivity functions of the four cones.

We find that this approach could explain ∼95% of the spectral and temporal variance of...