In insects the axons of primary olfactory receptor neurons terminate in specific glomeruli in the antennal lobe. Second order neurons relay this information to two higher olfactory centres, the mushroom body and the lateral horn, the special focus of this proposal. Functional inactivation and ablation of the mushroom body suggest that it is specific to olfactory learning, while the lateral horn is sufficient for more basic olfactory responses, including those which can be characterised as innate. Despite this importance, there is almost no structural and functional information on the third order neurons of the lateral horn. My research programme aims to generate a complete wiring diagram of the relevant neural circuits, characterise the receptive fields of these neurons and determine the cellular and circuit basis of the processing of olfactory information in this system. These scientific goals depend on a cross-disciplinary combination of molecular genetic techniques to label and stimulate identified neurons in the olfactory pathway, in vivo neurophysiology, optical stimulation and large-scale electron microscopy. One specific model system that I will use to address general questions of olfactory perception will be the study of sex-pheromone processing, where I have obtained new anatomical data that identify likely components of the pathway that turns smell into sex-specific behaviour. All these experiments will help us to understand how identified neurons integrate and transform specific odour information–the neural basis of olfactory perception. I hypothesise that by studying a discrete circuit down to the level of each identified neuron, I can new obtain new insights into information processing that will be of general relevance to neurobiology.