Interaction of optic flow and sky compass signals in the central complex of the desert locust Schistocerca gregaria

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Insects like vertebrates show sophisticated performance in spatial orientation and navigation. This includes seasonal migrations over thousands of kilometers and homing behavior in central-place foragers. Besides landmark- and sky compass orientation for determining navigational directions, a step counting mechanism (during walking) or an optic flow dependent mechanism is used by insects for distance estimation. Neurobiological data from various species increasingly point to a key role of the central complex in diverse navigational tasks. In the fly Drosophila the central complex plays a role in spatial memory, in directional decisions as well as in the coding of body orientation in space. Work from our own group in desert locusts have discovered a network of interneurons in the central complex, which encodes spatial orientations relative to sky compass signals, in particular the polarization pattern of the blue sky. In contrast, the central nervous monitoring and integration of distance information is largely unclear. In this project we want to bridge this gap by characterizing and indentifying neurons that respond specifically to visual flow fields and thus respond to signals that are relevant for distance estimation in flight. The project shall uncover, which neurons are optic-flow sensitive and how these signals are integrated with sky compass information. In a second part of the project, the role of GABAergic and tyraminergic signal transmission will be addressed. We will test the hypothesis that GABAergic neurons provide sky compass information to the central complex, whereas tyraminergic neurons provide optic flow input. Through pharmacological manipulation, the role of both transmitters will be studied on the physiology of central-complex neurons, and the role of GABA on polarotaxis behaviour. The proposed research is likely to uncover important aspects of central nervous control of spatial orientation in insects and will be a basis for computational models of spatial control.