PROJECT SUMMARY / ABSTRACT A fundamental function of the nervous system is to determine salience of sensory stimuli in the environment and accordingly regulate attentional response to them. Salience is dynamic. What is salient to an animal changes from moment to moment in accord with its experience and current physiological need. A prime example observed widely across species is the salience of food-associated stimuli. These stimuli are salient for food-deprived animals and therefore demand their attention. By contrast, food-associated stimuli lose their salience when animals become satiated. This indicates that neural circuits that control attentional behavior integrates the information of hunger and satiety. Appropriately determining salience based on current need and thereby regulating attention is essential for survival and its dysregulation is associated with neuropsychiatric disorders. However, it is not known what neural circuits mediate attentional behavior and how these circuits integrate internal information of hunger and satiety. Here we propose to use Drosophila as a model to dissect neural circuits that control attentional behavior to food-associated olfactory stimuli in accord with hunger and satiety. We employ a multidisciplinary approach that combines a novel behavioral assay, a novel bidirectional neural activity reporter, genetic and optogenetic manipulations, and in vivo recording of neural activity to test our hypothesis that a dopamine-modulated olfactory center, the mushroom body, plays a key role in appropriately computing salience of food-associated odors based on current hunger state. In Aim 1, we will establish that the salience of food odor is modulated by hunger state and will determine the role of mushroom body in generating attentional response to olfactory stimuli. In Aim 2, we will identify hunger-sensitive dopamine neurons, whose activity is modulated by signals reflecting hunger and satiety. In Aim 3, we will identify mushroom body output that integrates information of food odors and hunger state to drive attentional behavior. Together, our studies will reveal the neural mechanisms that regulate attentional behavior in response to food-associated odors in accord with hunger state. The functional organization of the Drosophila mushroom body exhibits remarkable similarity to that of the mammalian striatum and its dopamine input, and the dopamine circuits in mammals have long been implicated in computation of salience. Therefore, we expect that our project will contribute to providing an understanding of the operational principles of neural circuits that mediate salience determination.