Activity of a descending neuron associated with visually elicited flight saccades in Drosophila.

Approaching threats are perceived through visual looming, a rapid expansion of an image on the retina. Visual looming triggers defensive responses such as freezing, flight, turning, or take-off in a wide variety of organisms, from mice to fish to insects. In response to looming, flies perform rapid evasive turns known as saccades. Saccades can also be initiated spontaneously to change direction during flight. Two types of descending neurons (DNs), DNaX and DNb01, were previously shown to exhibit activity correlated with both spontaneous and looming-elicited saccades in Drosophila. As they do not receive direct input from the visual system, it has remained unclear how visually elicited flight turns are controlled by the nervous system. DNp03 receives input from looming-sensitive visual projection neurons and provides output to wing motor neurons and is therefore a promising candidate for controlling flight saccades. Using whole-cell patch-clamp recordings from DNp03 in head-fixed flying Drosophila, we showed that DNp03 responds to ipsilateral visual looming in a behavioral-state-dependent manner. We further explored how DNp03 activity relates to the variable behavioral output. Sustained DNp03 activity, persisting after the visual stimulus, was the strongest predictor of saccade execution. However, DNp03 activity alone cannot fully explain the variability in behavioral responses. Combined with optogenetic activation experiments during free flight, these results suggest an important but not exclusive role for DNp03 in controlling saccades, advancing our understanding of how visual information is transformed into motor commands for rapid evasive maneuvers in flying insects.