Neural circuits transform sensory information in the external world into abstract patterns of electrical activity in the brain to induce adaptive behavioural responses. The innate nature of many animal behaviours argues that their underlying circuits are specified by precise genetic programmes acting during development. Research in several model systems has contributed substantial insights into the genetic specification of neuron types, the mechanisms of neural guidance and wiring specificity, and the contribution of individual neural populations to specific animal behaviours. However, our understanding of the organisation of complete neural circuits – from sensory input to motor output – is very limited. This lack of knowledge has obscured a view of how genetic programmes may act coordinately in distinct neural lineages to specify a functionally integrated circuit. This Sinergia project aims to address the genetic basis of the formation and function of neural circuits through comprehensive characterisation of gustatory circuitry in the fruit fly, Drosophila melanogaster. Drosophila taste circuits offer a number of advantageous properties to tackle this fundamental problem. First, this sensory modality is relatively simple: as in vertebrates, gustatory perception in Drosophila comprises a limited number of sensory pathways underling distinct classes of tastants (e.g. sweet, bitter, salty). Second, taste stimuli evoke robust behavioural responses – notably extension or retraction of the proboscis (the main feeding organ of the fly) - that also reveal evidence of more sophisticated processing properties, such as adaptation and sensory integration. Third, the circuitry is likely quite shallow from sensory input to motoneuron output, with proboscis extension probably controlled by a limited number of interneurons residing entirely with the primary gustatory center, a part of the suboesophageal ganglion (SOG). Finally, the Drosophila model offers a powerful combination of genetic tools for precise spatial and temporal manipulation of gene and neuronal function, and access to high resolution cellular imaging, physiological analysis and quantitative behavioural assessment. Together, these offer unparalleled potential for dissection of the development, structure and function of neural circuits. The project has four specific aims.  First, generation of genetic tools for the analysis of gustatory circuitry.  Second, identification and mapping the elements of gustatory circuitry.  Third, structural identification and physiological characterisation of circuit elements and synaptic connectivity.  Forth genetic analysis of developmental specification and functional organisation in the taste circuit: towards a "developmental algorithm" for neural circuit formation. Together these aims will provide a comprehensive anatomical and functional map of gustatory processing pathways and insights into the cellular origins and genetic mechanisms by which individual circuit elements arise and wire together during development.