Meeting Abstract
Thorough characterization of the behavioral strategy by which animals search an environment and how this pattern is affected by sensory stimuli is an important step for understanding the neural processes that give rise to these behaviors. The Drosophila olfactory system is an excellent model organism to study these strategies because of its relative simplicity, the availability of genetic tools and because odors have a marked effect on its locomotion. In this study, we uncover the statistical nature of odor modulation of locomotion and propose a simple model that captures much of the variability in attraction. We created an 8 cm diameter circular arena with a 2.5 cm concentric circular region illuminated with red light. We expressed the red-light activated channelrhodopsin, Chrimson, under the control of Orco-Gal4 (Orco-Gal4; UAS-Chrimson) to activate a large fraction of all ORN classes in the presence of red light. These flies were previously reported to exhibit strong attraction to red light. We show that fly locomotion can be modeled as sequences of sharp turns, directed runs, and stops. We found that there are two mechanisms underlying attraction to odors: First, activation of ORNs changes the distribution of stops, runs and turns. These kinematic changes explain a small, but significant fraction of the attraction to odor. Second, and a far more important mechanism, is an increase in the density of sharp turns and tight control of turn direction around the light border. We then created a simple generative model of locomotion. The synthetic flies we generate using our model not only replicate the level of attraction, but also approximate the temporal progression of attraction in the presence of odor and the variability in attraction. These results have important implications for neural control of odor-modulation of locomotion.
