How does the Drosophila brain compute and see visual motion?

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Animals have neural mechanisms for detecting visual motion, enabling them to infer the speed and direction of objects that move in visual scenes. With its perceptual advantages the ability to detect motion has shaped the organisation and function of visual systems. However, the way in which the visual systems process and route motion information has proven to be a difficult problem to decipher. This proposal aims to elucidate the functional organisation of neural networks responsible for encoding visual motion in the brain of the fruit fly, Drosophila. We have recently developed an extremely versatile Drosophila preparation that enables us to visualise in real time how a specialised web of motion sensitive neurones (LPTCs) in the brains of transgenic flies translate moving images in the scene into neural activity patterns (calcium and voltage signals). These flies have genetically engineered eyes that are sensitive to ultraviolet (UV) light and brains that express green-sensitive fluorescence proteins (optical reporters) that react to changes in the neural activity (here calcium changes) in LPTCs. Since the spectral sensitivities of the eye and optical reporters do not overlap, we can visualise neural activity in the LPTCs when such a fly looks at moving objects, being oblivious of us simultaneously scanning its brain. In order to fully utilise this novel preparation requires the generation of a unique hybrid experimental apparatus that can visualise calcium signals and measure voltage responses with sharp microelectrodes simultaneously. For live imaging the flies will be placed in this apparatus in which they are presented with moving UV-light patterns while calcium and voltage signals are monitored from the LPTCs. Using this system, together with further genetic modifications in the eyes and the brain of the flies, we wish to investigate how visual motion signals are routed and processed by the fly's visual system. Here we plan to find answers to two important open questions. What is the contribution of different photoreceptor types in routing visual information to the brain so that the speed and direction of objects moving in the scene can be inferred? and what is the contribution of attentional signals from the brain in the visual motion processing? These questions will be studied by monitoring changes in calcium and voltage signals of LPTCs in transgenic flies in which selective neural pathways from the eyes or from the brain can be turned on and off, using temperature-sensitive genetic switches. Furthermore, the visual behaviour of the same flies will be characterised in a flight simulator system running in our laboratory. In this way we shall be able to correlate the genetically targeted changes in the routing and processing of visual motion information to the animal behaviour and cognitive phenomena. In a parallel approach, the results from these experiments will be analysed and modelled mathematically to find answers to the open question of how moving visual objects in the scene are encoded into moving neural images, as represented by activity patterns of networks of interconnected neurones in the brain.