The integration of visual and haltere feedback in Drosophila flight control

To control complex motor behaviors, animals often rely on feedback from several different sensory modalities. There has been extensive research on the role of individual sensory systems during sensory-motor reflexes; however, less is known about the convergence of multiple modalities onto a common motor pathway. The fruit fly, Drosophila melanogaster, relies on many sensory inputs to control a small number of flight muscles, making it an excellent model for studying multi-sensory integration.;Fruit flies are equipped with two sensory organs that encode angular velocity cues during flight: the compound eyes and the mechanosensory halteres. The research in this dissertation focuses on the roles these two sensory modalities play in flight control. To study this interaction, I developed a flight simulator for the fruit fly. This instrument enabled me to stimulate the halteres and the visual system separately and concurrently, while measuring the resultant changes in wingbeat amplitude.;The first step in studying the flight control system was to determine the bandwidth of each sensory modality separately, since inherent differences in their mechanisms of transduction would imply different temporal responses. I measured the frequency responses for both the visual system and the halteres. The results show that visually elicited behavioral responses are strongest for relatively slow rotations whereas haltere-mediated responses to mechanical rotation increase with rising angular velocity. Combining input from both systems may enable the fly to maintain sensitivity without limiting bandwidth.;I next studied how the two feedback channels were combined during simultaneous stimulation, as occurs during free flight. I determined the contribution of each sensory modality by measuring the response to concurrent visual and mechanical oscillations, which varied in amplitude, phase, and axis of rotation. The results of these experiments provide strong evidence that: (1) the flight control system uses a weighted sum of the two sensory inputs, and (2) these weights favor feedback from the haltere system. Finally, a model was developed based on these experimental findings, and was validated using a simulation. In summary, the research in this dissertation presents a framework for describing the role of multi-sensory inputs in the control of complex motor behaviors.