Flies adaptively control flight to compensate for added inertia

Animal locomotion is highly adaptive, displaying a large degree of flexibility, yet how this flexibility arises from the integration of mechanics, sensing and neural control remains elusive. Animals experience significant fluctuations in weight throughout their lifetime, which require flexible strategies to maintain performance as changes in mass or inertia impact stability. Compensatory strategies are especially critical for animals that rely on flight for survival. To shed light on these strategies, we implemented a control theoretic framework to study how fruit flies (Drosophila) compensate for added rotational inertia. Flies with added inertia were placed inside a virtual reality arena which enabled free rotation about the vertical (yaw) axis. Adding inertia increased the fly’s response time yet had little influence on overall gaze performance. Flies maintained stability following the addition of inertia by adaptively modulating both visuomotor gain and damping. In contrast, mathematical modeling predicted a significant decrease in flight stability and performance. Adding inertia altered saccades, however flies compensated for the added inertia by increasing yaw torque production, indicating that flies sense that they are mechanically loaded. Taken together, in response to added inertia flies trade off reaction time to maintain flight performance through adaptive neural modulation. Our work highlights the flexibility of motor control in flight.