TAMMERO,L.F.*; DICKINSON,M.H.: The Pattern of Optic Flow Determines Flight Behavior in Freely Flying Drosophila

While flying through its environment in search of food, a fruitfly (Drosophila) must integrate input from several sensory modalities. To study the behavioral patterns that emerge from the interactions of these sensory systems, we reconstructed three-dimensional trajectories from images taken by stereo infrared video cameras during free flight within a controlled arena. Flies move through their environment using a series of straight flight segments separated by rapid turns called saccades. Analysis of the trajectories suggests that saccades are fixed motor patterns that alter course by approximately 90 degrees. For eachposition in the flight trajectory, we calculated the fly’s angular and translational velocities and reconstructed the visual environment from the fly’s perspective. From these reconstructions, we determined the optic flow experienced by the fly during the course of its flight. Analysis of these data suggests that optic flow does not alter course direction during the straight segments and that the mechanosensory halteres, which act as an inertial guidance system, dominate this portion of free flight behavior. However, reverse correlations of the spatially integrated optic flow suggest that image expansion is the signal that triggers saccades. In summary, our data suggest that complex behavioral patterns seen during free flight emerge from interactions between the flight control system and the visual environment.