Sparse Neural and Motor Networks Underlying Control in the Drosophila Flight System

Citation

de Souza, Alysha Maria (2022) Sparse Neural and Motor Networks Underlying Control in the Drosophila Flight System. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/part-mf19. https://resolver.caltech.edu/CaltechTHESIS:10312021-193119771

Abstract

We often look to the natural world for inspiration in design and engineering. The fruit fly, Drosophila melanogaster, with approximately 100,000 neurons in its central nervous system (CNS) versus the roughly 100 billion neurons of the human brain, is relatively uncompromising in the richness of behaviors it is capable of performing given its comparatively sparse nervous system. It exhibits exceptional aerial agility, despite the steep aerodynamic constraints of miniaturization thanks to unique physiological and biomechanical thoracic adaptations. However, the mechanisms governing its sparse and precise flight control have remained largely inaccessible due to technological and geometric limitations, leaving many long-standing questions in the field of insect flight control unexplored. Recent advances in the field of molecular biology have created a vast toolkit for both optical imaging and genetic manipulation of cellular function. This revolution of genetic advances allows us to visualize changes in muscle activity in situ as fluorescent signals, to record from fluorescently targeted cells via electrophysiology or 2-photon imaging, and to optogenetically activate or silence the activity of targeted cells. This thesis utilizes recent technological and molecular advances to probe three key aspects of fly flight control: 1) the dynamic interactions of flight steering muscles to produce flight maneuvers, 2) the source of timing information for the structuring of the the motor phase code, an extremely temporally precise wingbeat-synchronous aspect neural firing, and 3) the mechanisms by which slow, graded descending visual process recruit the flight muscles.

In the contents of the ensuing chapters I propose mechanisms for flight control pertaining to the wing muscles as well as their inputs. First, I describe the activities of each of the flight steering muscles in response to visual motion to generate movement in yaw, pitch, and roll (Chapter II). I then characterize the flexible individual dynamics and combinatorial timing of the system, and propose specific mechanisms by which interneurons rather than muscle physiology govern these adaptable firing patterns according to sensory inputs(Chapter II). Sensory inputs within this thesis take two forms: thoracic mechanosensory and timing information as well as descending visual input. I characterize mechanosensory and timing adaptations of an evolutionarily evolved hind wing, as well as the impact of haltere feedback to flight control (Chapter III). Lastly, I propose a mechanism by which descending visual commands produce graded outputs of the muscles.

Thesis Files