Responses of a locust visual interneuron correlate with simple and compound object motion within the vertical plane.

Animals living in complex visual environments must contend with multiple visual cues that signal potential threats by detecting approaching objects and generating adaptive avoidance responses. One collision detection system in locusts is composed of the lobula giant movement detector (LGMD) and its postsynaptic partner, the descending contralateral movement detector (DCMD). Extensive work on this pathway has revealed that it is preferentially selective to visual stimuli generated by an approaching object (looming) and triggers avoidance behaviours such as jumping and flight steering. Recent work has shown that this pathway also responds characteristically to complex object motion that includes trajectory changes in the horizontal plane. To test the hypothesis that responses of this pathway correlate to motion in the vertical plane, we recorded from the DCMD while presenting combinations of simple looming as well as translation and transitions from and to looming. We found that the DCMD responses occurred earlier and were more robust for vertical translation in the lateral visual field, perpendicular to the centre of the eye. We also found strong correlations for the timing and firing rate as well as the duration and number of spikes of described phases of the response. These findings fit with our existing understanding of how this pathway conveys visual information to downstream elements initiating and controlling escape behaviours and provide further information on how this tractable system adds to our understanding of fundamental mechanisms that underly visually evoked behaviours.