Functional imaging from the muscles of the fruit fly wing-hinge during tethered flight

Abstract

Animal movement emerges from a system of inner and outer-feedback loops by which sensory information directs and stabilizes motor output. Compared to our knowledge of coding within sensory systems, our understanding of how motor codes produce locomotion remains poorly understood. The agile aerial behaviors of flies present a prime example of this problem: using subtle changes in wing kinematics, flies respond to visual input and execute hairpin turns in milliseconds. Although flies are equipped with relatively few muscles with which to regulate wing motion, they nevertheless execute very precise maneuvers. As in other flies, in the fruit fly, Drosophila melanogaster, the 15 tiny control muscles of each wing are anatomically grouped according to the skeletal elements within the wing hinge on which they insert: the first, third, and fourth axillary sclerites and the basalare. Prior studies have recorded the activation of a small subset of these muscles during flight behaviors using fine metal electrodes however, the activity of the entire population has not been observed due the small size of most muscles and their complex overlapping pattern of insertion. To overcome these limitations, we expressed a genetically-encoded calcium indicator (GCaMP6f) in the steering muscles of Drosophila, and imaged their activity through the intact thorax of tethered, flying flies. During flight, activity was distributed broadly across the entire population of steering muscles. By presenting the flies with a set of large field visual motion, we have begun to map the tuning of individual muscles and muscle groups to the control of body translation and rotation during flight.

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