Abstract

SummaryLike many insect species, Drosophila melanogaster are capable of maintaining a stable flight trajectory for periods lasting up to several hours1,2. Because aerodynamic torque is roughly proportional to the fifth power of wing length3, even small asymmetries in wing size require the maintenance of subtle bilateral differences in flapping motion to maintain a stable path. Flies can even fly straight after losing half of a wing, a feat they accomplish via very large, sustained kinematic changes to both the damaged and intact wings4. Thus, the neural network responsible for stable flight must be capable of sustaining fine-scaled control over wing motion across a large dynamic range. In this paper, we describe an unusual type of descending neuron (DNg02) that projects directly from visual output regions of the brain to the dorsal flight neuropil of the ventral nerve cord. Unlike many descending neurons, which exist as single bilateral pairs with unique morphology, there is a population of at least 15 DNg02 cell pairs with nearly identical shape. By optogenetically activating different numbers of DNg02 cells, we demonstrate that these neurons regulate wingbeat amplitude over a wide dynamic range via a population code. Using 2-photon functional imaging, we show that DNg02 cells are responsive to visual motion during flight in a manner that would make them well suited to continuously regulate bilateral changes in wing kinematics. Collectively, we have identified a critical set of DNs that provide the sensitivity and dynamic range required for flight control.

Highlights

  • The DNg02s were previously identified anatomically[6] and consist of a cluster of at least 15 cell pairs with morphology that is not distinguishable at the level of light microscopy, the largest of the population-type class of descending neurons (DNs) identified so far

  • Within a fly’s nervous system, sensory information from the brain is conveyed to motor regions of the ventral nerve cord (VNC) by several hundred pairs of descending neurons (DNs) that are roughly stratified into a dorsal pathway that projects to flight motor neuropils and a ventral pathway that projects to leg neuromeres[5,6] (Figures 1A and 1B)

  • The flies flew under closed-loop visual conditions in which they controlled the angular velocity of striped drum, we presented brief, 100-ms pulses of 617-nm light to activate the targeted DNs (Figures 1C and 1D)

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Summary

Introduction

The DNg02s were previously identified anatomically[6] and consist of a cluster of at least 15 cell pairs with morphology that is not distinguishable at the level of light microscopy, the largest of the population-type class of DNs identified so far. Their small, spindly cell bodies reside in a cluster at the ventral edge of the gnathal ganglion (GNG; Figure 2A). The primary neurites of the DNg02s run ventrally along the edge of the GNG before taking a hairpin turn and ascending dorsally, where each cell arborizes in a hemicircle around the esophagea

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