Motor neurons organize Drosophila feeding sequences via a disinhibitory cascade

Classical models view motor neurons as the final relays of commands driving behaviors such as breathing and feeding. Here, in simultaneous quadruple-electrode recordings from Drosophila performing feeding behavior, we demonstrate that the relevant motor neurons directly coordinate sequential muscle activity through a propagating feedforward disinhibition cascade. Food stimuli trigger rhythmic firing in a leading motor neuron, causing it to release glutamate and thereby simultaneously excite its target muscle and disinhibit a premotor neuron. This disinhibition recruits the next motor neuron in the sequence, triggering a wave that propagates with millisecond precision down the motor chain. By incorporating behavior analysis and computational modeling, we further show that this patterned circuit activity is independent of the pumping rate, enabling this circuit to support robust behavior in the face of changing action contexts. Our work expands the known roles of motor neurons to include the active patterning of precisely ordered motor output.