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From the eye to the brain: understanding light, colour vision and behaviour

Sussex scientists have studied how zebrafish send information from the eye to the brain to explore unanswered questions about colour vision and behaviour.

The researchers, led by Professor Tom Baden, focussed on Retinal Ganglion Cells (RGCs); the neurons responsible for passing information from the eye to the brain.

In their paper published this week in Current Biology, they revealed that the structure and function of the RGCs in zebrafish are highly position dependent.

For instance, they demonstrated that the RGCs in the ‘acute zone’ of the retina (where visual acuity is at its highest) are particularly responsive to ultraviolet (UV)-bright stimuli. This is likely an important factor in predatory behaviour, as zebrafish eat tiny zooplankton that sparkle brightly in UV when illuminated by the sun.

This finding compliments the researchers’ recent discovery that zebrafish are able to use a single UV-sensitive photoreceptor to spot this tiny prey.

Professor Baden said: “By furthering our understanding of RGCs, we can better understand what visual input the brain receives and how this leads to certain behaviours. By doing this in fish, and then linking it to circuits in mammals, this has the potential to teach us about the evolution of our own vision.

“Throughout our lab’s research, we consistently find that different functions sit in different parts of the eye. Essentially it means zebrafish see differently in different parts of visual space. It is a trick to match the eye’s capabilities to things encountered in the wild. For example, underwater when looking straight up, you see only black/white silhouettes, so fish have evolved to be effectively colour blind in the corresponding part of the eye, as colour vision here would be largely pointless.”

Zebrafish, like many other species of fish as well as most birds, reptiles and some amphibians, have tetrachromatic vision. This means that as well as the red, green and blue vision that humans have, they are also able to see in UV.

The researchers studied how the retina processes signals from these four ‘colour channels’ and found it is much more complex than in humans. Red/green vision in the fish is essentially synonymous with black and white vision, while blue vision is more complicated and may serve as a background signal. UV vision, as described, is almost certainly linked to prey capture, but may also have additional specific uses such as predator detection.

This research was conducted in collaboration with the Hong Kong University of Science and Technology, through a joint PhD programme.

The article “Zebrafish retinal ganglion cells asymmetrically encode spectral and temporal information across visual space is published in Current Biology.

By: Luke Churchill
Last updated: Wednesday, 17 June 2020