The role of recurrent long- and short-range connections in experience-dependent modulation in Drosophila

During its life an animal is constantly exposed to a plethora of olfactory inputs, many of them being essential for the animal’s survival and reproduction. While certain odours induce an innate and stereotyped behavioural output, odour-based behavioural decisions are largely modulated by physiological state, specific context and previous experience. Our recent data reveal that odour-evoked responses of projection neurons (analogous to mitral cells) are strongly modulated by associative olfactory learning in primary (i.e. antennal lobe, AL) as well as secondary (i.e. lateral horn, LH) olfactory brain centres in Drosophila. Since learning crucially depends on the mushroom body (MB), a well described centre for learning and memory, we hypothesize that experience-dependent modulation is mediated by centrifugal (i.e. long-range) connections between different brain centres (MB/LH AL) as well as other recurrent connections (i.e. short-range) within and between those respective neuropils (e.g. MB LH). To comprehensively study experience-dependent modulation along the olfactory circuitry, we will employ classical learning paradigms, but also establish novel learning assays that include an ecological relevant context, such as oviposition and mating. The goal of TP8 is (1) to provide a basic and comprehensive characterization of learning-induced changes in different neuronal populations at primary and secondary olfactory centres, and (2) to establish a mechanistic understanding about how centrifugal and other recurrent connections modulate odour representations depending on previous experience and ecological context in the fly brain.