Complex motion trajectories are represented by a population code from the ensemble activity of multiple motion-sensitive descending interneurons in locusts

Adaptive locust flight relies on rapid detection and processing of objects moving in the visual field. One identified neural pathway, comprised of the lobula giant movement detector (LGMD) and the descending contralateral movement detector (DCMD), responds preferentially to approaching objects. The LGMD receives retinotopic inputs from ipsilateral ommatidia and generates spikes in a 1:1 ratio in the DCMD, which synapses contralaterally with multiple locomotion-related neurons. Other motion-sensitive neurons have also been identified in locusts but are not as well characterized. To better understand how locusts process visual information, we used multichannel neural recordings within a stimulus arena and presented various complex visual stimuli to investigate the neural encoding of complex object motion. We found multiple discriminated units that responded uniquely to visual motion and categorized the responses. More units responded to motion trajectories with a looming component, compared to translations across the visual field. Dynamic factor analysis (DFA) of discriminated units revealed common trends that reflect the activity of neural ensembles. The numbers and types of common trends varied among motion trajectories. These results increase the understanding of complex visual motion processing in this tractable system.