Biology subjects

Fornetto, C.

Publications and source records attributed to Fornetto, C..

2 recordsLinked to original sources

bioRxiv2026

On-Off coding is latent in vertebrate visual circuits

Across sensory systems, neurons often encode stimulus changes of opposite sign as On and Off signals, a fundamental strategy for representing deviations from baseline. In vertebrate vision, this computation is classically attributed to an early, hardwired split in the retina, with segregated pathways subsequently propagated through downstream circuits. Here, we challenge this view. Combining comparative transcriptomics, pharmacology, genetics, in vivo imaging and electrophysiology in zebrafish, with validation in mouse retina, we show that On-Off coding is a latent and intrinsic property of visual circuits. Bipolar cells frequently co-express receptor systems of opposing polarity and can generate mixed responses that are normally suppressed by inhibitory circuitry. Disrupting inhibition or selectively blocking receptor pathways unmasks robust On-Off signalling. In addition, mixed On-Off responses emerge naturally as effective light input increases, including during development and at higher light levels. Across processing stages, including retinal ganglion cells and central neurons, inhibition repeatedly enforces apparent polarity segregation. Thus, polarity splitting is a distributed, dynamically regulated computation rather than a fixed circuit feature. HIGHLIGHTSO_LIMixed On-Off signals are latent across visual processing stages C_LIO_LIInhibition actively sculpts polarity, not just refines it C_LIO_LIPolarity splitting is a dynamic, distributed and reusable computation C_LIO_LIConserved mechanism revealed in zebrafish and mouse C_LI

neuroscience↗

bioRxiv2024

Vertebrate vision is ancestrally based on competing cone circuits

Vision first evolved in the water, where light becomes increasingly monochromatic with viewing distance. The presence of spectrally broad ( white) light is therefore the exclusive remit of the visual foreground. However, if and how aquatic visual systems exploit this white effect as an inductive bias, for example to judge distance, remains unknown. By combining two-photon imaging with hyperspectral stimulation, genetic cone-type ablation, and behaviour, we here show that zebrafish suppress neural responses to the visual background by contrasting greyscale and colour circuits that emerge at the first synapse of vision. To do so, zebrafish use an early retinal architecture that fundamentally differs from that of mammals: Rather than combining cone signals to drive the retinal output leading to behaviour, zebrafish vision is built around competing ancestral cone systems: Red/UV versus green/blue. Of these, the non-opponent red and UV cones, which are retained in mammals, are necessary and sufficient for vision. By contrast, the colour opponent green and blue cones, which are lost in mammals, form a net-suppressive auxiliary system that shape the core drive from red and UV cones. Our insights challenge the long-held notions that cones act in concert to drive visual behaviour, and that their spectral diversity primarily serves colour vision. Instead, we posit that vertebrate vision is ancestrally built upon opposing cone systems that emerged to exploit the strong spectral interactions of light with water. This alternative view points at terrestrialisation, not nocturnalisation, as the leading driver for visual circuit reorganisation in mammals.

neuroscience↗