Understanding how neural circuits control arm and leg movements is a major challenge in neuroscience with implications for treating movement disorders, designing neural prostheses, and robotics. Even seemingly simple, everyday movements such as walking rely on the integrated activity of complex circuits that span multiple levels of the nervous system. High-level circuits in the brain generate movement instructions, such as when to start moving and how fast to move. Low-level circuits in the spinal cord (in vertebrates) or ventral nerve cord (in invertebrates) integrate these instructions to generate appropriate activation patterns for muscles. The instructions are encoded by a small number of descending neurons, which form a critical link between the brain and the body. In this project, we addressed two major open questions related to descending neurons: how brain circuits are organized to recruit descending neurons for a specific motor task in a context-appropriate manner, and how low-level circuits translate descending neuron instructions into coordinated limb movement. To tackle these questions, we took advantage of the powerful experimental tools available for the compact nervous system of the fruit fly, Drosophila melanogaster, including connectomics, optogenetics, and neural recordings in behaving animals. The fly’s neural circuits controlling the limbs are more tractable and experimentally accessible than those of vertebrates, but still similar in their basic organization and function. This suggests that the motor control principles discovered in the fly will be highly relevant to motor control in other animals, including mammals.
