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Importance of colour saliency in Drosophila melanogaster

Supervisor: Trevor Wardill

The fruit fly is a key model in vision research. Its small brain and compact neural circuits can be manipulated by sophisticated genetic tools, making it possible to dissect the neuronal machinery underlying vision. Colour vision provides signals that improve object saliency in natural environments, but little is known how they are processed and alter attention. While a spectral comparison is made between rod and cone vertebrate photoreceptors (Joesch & Meister 2016), the spectral comparisons made in invertebrates remains obscure. This project will aim to quantify neural activity and identify the computations that transform colour sensory inputs into visual perceptions and the output signals used to drive behaviour.

To determine computational strategies, a combination of genetic, imaging, electrophysiological and behavioural methodologies is required. Head-fixed flies will be presented with custom panoramic visual stimuli of moving patterns and colour. Simultaneously their neural activity will be monitored with 2-photon imaging of fluorescently reported calcium dynamics (Chen et al. 2014). Matlab, will coordinate the testing process for specific contrasts, colours, patterns, centre-surround ratios, angles, velocities and natural scenes. Specific neuron populations will be labelled with fluorescent neural activity indicators using genetic targeting.

Head-fixed animals will also undertake behavioural navigational tasks by placing them in a virtual reality (VR) arena, monitoring their movements with specialised tracking system and externally modulating neural activity in visual circuits using a red-shifted channel rhodopsin (that does not distract the animal). Through this VR paradigm we will use naturalistic stimuli to closely mimic visual behaviour in the wild.

Relevant references

Chen T-W, Wardill TJ, Sun Y, et al. 2013. Ultra-sensitive fluorescent protein sensors for neural activity. Nature 499: 295-300.

Joesch M & Meister M 2016. A neuronal circuit for colour vision based on rod–cone opponency. Nature 236: 236-239.

Schnaitmann C, Garbers C, Wachtler T and Tanimoto H 2013. Colour Discrimination with Broadband Photoreceptors. Current Biology 23: 2375-2382.

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