The brain of a fly is capable of steering the animal through a complex environment at high relative speeds, avoiding stationary obstacles and moving predators. Because it is relatively easy to study how flies do this at several levels, from the behavioral to the cellular, fly vision has long been recognized as an ideal system to address a fundamental question in neuroscience- how does the distributed activity of neurons orchestrate animal-environment interactions to result in successful coordinated behavior? This work addresses this basic question with two related studies. The first concerns higher levels of visual processing and behavior. Do flies build a neural representation of nearby objects or, alternatively, is flight governed by a direct coupling of visual input into motor commands? The second identifies specific neurons responsible for visual guidance behaviors.This work involves the establishment of a new research activity in the EU by a Principal Investigator who is moving from a third country (the US) into the EU. It uses a unique high-throughput, virtual reality free flight arena in which flies are tracked in realtime by a computer vision system. With this technology, physically unmanipulated and unrestrained flies are automatically and repeatedly presented with arbitrary visual stimuli projected on the arena walls and floor. Thousands of digitized 3D flight trajectories are gathered, and behavioral experiments using this system will be combined with targeted genetic manipulation of the nervous system and analyzed to reveal the magnitude and reliability of effects. This will be accomplished by using molecular genetic techniques to selectively perturb individually identified neurons in the brain and measuring the effect on flight control in response to precisely specified visual stimuli. Thus, by utilizing controlled stimulus conditions and measuring behavioral responses in detail, the results will show the contribution of individual neurons to behavior.