TOWARDS AN UNDERSTANDING OF NEUROMUSCULAR IMPLEMENTATION OF BODY ROLL CONTROL IN FREE-FLYING DROSOPHILA
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Anyone who has ever stood on one foot or tried to balance a pencil at tip of their index finger knows that stabilizing a dynamically unstable system is an active, and sometimes difficult task. Drosophila melanogaster, the humble fruit fly, experiences this daily--flapping flight is inherently dynamically unstable, and flies must navigate an unpredictable environment filled with wind gusts, fly swatters, and predators. Of all these instabilities, rotations about the body roll axis have the shortest timescale for instability. A fly which does not begin to correct its roll posture within 1-2 wingbeats after a perturbation risks spiraling out of the air. How is this remarkably fast and precise control implemented in the neuromuscular system of the fly? In this work, I seek the answer to that question by leveraging a broad range of tools available to drosophila researchers: full wing and body reconstructions of freely flying flies recorded at high speed, targeted genetic manipulations via the GAL4/UAS system, optogenetic perturbations to motor neurons mid-flight, connectomic analyses to trace the pathways from sensory inputs to motor outputs, and quasisteady aerodynamic calculations disentangle the contributions of individual wing kinematic changes to free-flight roll stability. The picture that emerges is one of a robust, redundant system, in which multiple muscles within the sparse wing steering system are controlled together in order to ensure robust performance even in the event of loss of function of one of the constituent muscles. Beyond my free flight results, I also introduce designs for an updated magnotether apparatus which will enable the imaging of brain activity in a freely rotating tethered fly. Those experiments will begin to elucidate how the same stability reflexes studied in free flight are incorporated into navigational and heading representations within the fly brain. Developing a sound understanding of the muscular control of flight behavior paves the way for future work to further decode the workings of this complex system, in areas such as sensory integration, action selection, and recovery after injury.