Electrophysiological Analysis of Olfactory Representations in Drosophila

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 DESCRIPTION (provided by applicant): All sensory circuits, including the olfactory system, ascend from the sensory periphery to higher brain areas where stimuli are represented in sparse, stimulus-specific activity patterns. This sparse format is useful for accurate memory formation and retrieval. However, these specific signals must converge at some downstream site, given the limited numbers of motor neurons that represent the ultimate output of the circuit. We know very little about sensory processing downstream of sparse representations, on the converging side of neural networks. The Drosophila mushroom body (MB) has been an important model system for studying sparse representations in the olfactory system. New genetic labeling tools have revealed that the 2000 Kenyon cells (KCs) of the MB converge down onto a total of only 35 MB Output Neurons (MBONs). We will use these new tools to target MBONs for both electrophysiological recordings and calcium imaging, to examine nearly the entire layer of the network where the transition from sensory to motor begins. Using imaging to get a population-level view of activity patterns, we will determine how odor representations are reformatted as the circuit transitions from KCs to MBONs. Many of the MBONs are uniquely identifiable using these genetic labels. This enables us to compare their response properties of the same neuron across flies that have had different types of olfactory experience, to examine how plasticity shapes odor representations at this layer. Additionally, the neuromodulator dopamine is thought to play an important role in signal transmission across the KC-MBON synapse. By optogenetically controlling these specific dopaminergic inputs, we can examine how this neuromodulator regulates the flow of olfactory information across this layer of the circuit. Insights from this work will provide an important conceptual framework to understand how sensory perception is turned into action, and potentially contribute to our understanding of how sensory-motor coupling is impaired in disease states such as Parkinson's.