Uncovering the Neural Basis of Flight Control in Fruit Flies*

Rapidly-diverging aerodynamic instabilities require that flapping insects make subtle, millisecond-timescale adjustments to their wing motion to stay on course. Remarkably, fruit flies accomplish this feat using only 12 steering muscles to modulate the kinematics of each wing. Previous studies showed these stabilization reflexes can be modeled by a proportional-integral (PI) controller, but the implementation of this control by the wing muscles is poorly understood. Here, we leverage genetic tools for probing the fly nervous system and behavioral modeling to uncover the role of the first basalar (b1) muscle—a prominent member of the fly’s steering muscles—in the flight stabilization reflex. We selectively reduced the activity of the b1 muscle by silencing its motor neuron, and tested the control reflex of freely-flying flies. We find a surprisingly specific result: inhibiting b1 activity only affected the controller’s dependence on angular displacement, but not angular velocity, and this effect is specific to only one of the fly’s three rotational axes. What emerges from these and other studies is an organizational principal that dedicates different muscles to specific aspects of flight control.