Most vertebrates, including humans, cannot ‘see colour in the dark’ because the retinal rod photoreceptors that mediate vision in dim light usually come in a single spectral flavour (“green”), precluding spectral comparisons. But frogs and some salamanders have an additional ”blue”-rod type, potentially allowing for purely rod-based colour discrimination. Using behaviour, I recently demonstrated that this is indeed the case: frogs do make spectral comparisons down to the absolute visual sensitivity threshold. However, the ecological relevance of nocturnal colour vision and the structure and function of the retinal circuitry underlying rod-rod spectral comparisons, and enabling the simultaneous preservation of sensitivity and spectral resolution, have not been explored.
Thus, this proposal seeks to establish the purpose as well as the underlying retinal physiology and circuit implementation of frog colour discrimination near the visual threshold. For this, we will combine natural scene imaging, high-throughput multi-electrode array recordings from 1,000s of retinal ganglion cells and synaptic-resolution serial section electron microscopy of the blue-sensitive rod circuitry. This will enable unraveling which visual information is available to be used, and how it is processed, to reach the low-light limits of colour discrimination performance available to the vertebrate eye. Our research will also provide a link between the more intensely studied retinal circuits of fish and mammals, providing important insights about the evolution of vertebrate retinal networks’ architecture and computations. Finally, the topic of ‘colour vision in the dark’ is one that attracts considerable public interest, so this project will create valuable opportunities for public engagement with the research supported by the European Commission.
Fields of science
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