Sustained activity in a descending neuron is associated with flight saccades in Drosophila

Flies perform rapid turns termed saccades to change direction during flight. Evasive turns can be elicited by looming stimuli mimicking an approaching object such as a potential predator. Whereas projection neurons of the optic lobes responsive to looming stimuli have been well described, how this information is transmitted to the motor system to elicit a saccade is not well understood. Here we describe activity of the descending neuron DNp03 in Drosophila, which receives direct input from looming-sensitive visual interneurons and projects to wing motor areas within the ventral nerve cord. Whole-cell patch-clamp recordings from this neuron during head-fixed flight confirm that DNp03 is responsive to looming stimuli on the side ipsilateral to its dendrites. In addition, activity of this neuron is state-dependent as looming stimuli only elicit spikes during flight and not rest. The behavior in response to the looming stimulus is variable, which allowed us to study how activity of DNp03 relates to the execution of a saccade. Our analysis revealed that sustained activity in DNp03, persisting even after the visual stimulus ended, was the strongest predictor of saccade execution, therefore reflecting the behavioral decision of the fly to respond to the stimulus.