Colourfulness as a possible measure of object proximity in the larval zebrafish brain

Abstract

Summary The encoding of light increments and decrements by separate On- and Off- systems is a fundamental ingredient of vision, which supports edge detection and makes efficient use of the limited dynamic range of visual neurons 1 . Theory predicts that the neural representation of On- and Off-signals should be balanced, including across an animal’s visible spectrum. Here we find that larval zebrafish violate this textbook expectation: in the zebrafish brain, UV-stimulation near exclusively gives On-responses, blue/green stimulation mostly Off-responses, and red-light alone elicits approximately balanced On- and Off-responses (see also references 2 , 3 , 4 ). We link these findings to zebrafish visual ecology, and suggest that the observed spectral tuning boosts the encoding of object ‘colourfulness’, which correlates with object proximity in their underwater world 5 .

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

“… 48 Whether and how the larval zebrafish BCs’ axes are preserved, diversified, or even lost in downstream circuits will be important to explore in the future. In this regard, both retinal ganglion cells 21 , 22 and brain circuits 21 , 49 do carry diverse spectral signals; however, beyond a global overview, 29 the nature and distribution of their spectral zero crossings remain largely unexplored.

Figure 7 Possible links across vertebrate retinal color circuits Conceptual summary schematics of retinal circuits for color vision in zebrafish (A); dichromatic mammals, such as many rodents (B); and some trichromatic old-world monkeys, such as humans (C).

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“…48 Whether and how the larval zebrafish BCs' axes are preserved, diversified, or even lost in downstream circuits will be important to explore in the future. In this regard, both retinal ganglion cells 21,22 and brain circuits 21,49 do carry diverse spectral signals; however, beyond a global overview, 29 the nature and distribution of their spectral zero crossings remain largely unexplored.…”

“…The transformed time-traces were clustered using the scikit-learn (Python 3, Anaconda) implementation of the Gaussian Mixture Models algorithm. The number of clusters (29) was determined using the Bayesian information criterion (BIC). However, the BIC curve notably flattened above $20 clusters, suggesting that a range of solutions would be similarly plausible.…”

“…For this, we used two-photon (2P) imaging to measure spatially widefield but spectrally highly resolved tuning functions at the level of retinal bipolar cell (BCs) presynaptic terminals in the inner retina. This strategy was previously used to establish the spectral tunings of the cones, 27 , 29 thus facilitating direct comparison.…”

Tadpole Responses to Environments With Limited Visibility: What We (Don’t) Know and Perspectives for a Sharper Future

“…As turbidity interferes with color vision (Wilkins et al, 2016), its fluctuations can impact the interpretation of color as (including, but not limited to) a proxy for distance (Bartel et al, 2021). Until now, the change of color-based signals in response to visually challenging environments has been demonstrated only in a handful of studies, and limited to the context of adult signaling.…”