Neural dynamics for working memory and evidence integration during olfactory navigation in Drosophila

To navigate towards an unknown food source, animals must accumulate evidence about the location of a goal and store this information in working memory. Here we identify a population of local neurons in the fan-shaped body of Drosophila that exhibits both evidence integration and working memory dynamics. Imaging from these neurons during virtual odor-guided navigation reveals a bump of activity that is activated by odor, but can outlast the odor stimulus by several seconds. Persistent bump activity is associated with persistent movement in the direction adopted during odor, arguing that these neurons represent a directional working memory. When the fly navigates a virtual odor plume, bump activity slowly ramps up with successive odor encounters, indicating that it integrates odor information over time. We do not observe these dynamics in a set of neighboring local neurons, although both populations show slow modulation correlated with engagement in the task. Silencing the first population impairs the integration of odor encounters and the persistence of upwind heading. Our work identifies a small group of genetically-identified neurons that integrate and store stochastic sensory evidence to support navigation in complex natural environments.