Meeting Abstract
Locusta migratoria is an established neuroethological system for the study of sensory coding within a well-defined motion-sensitive visual neural pathway consisting of two identified interneurons, the Lobula Giant Movement Detector (LGMD) and its postsynaptic partner, the Descending Contralateral Movement Detector (DCMD). The DCMD connects to thoracic interneurons and motor neurons and is implicated in initiating and coordinating avoidance behaviours. This pathway responds robustly to visual motion that occurs in the locust’s natural environment. It is most sensitive to motion of objects approaching on a collision course and can also track changes in object trajectory and motion of multiple objects within the visual field. However, it is not known if this pathway responds to objects that change approach velocity, which could be encountered during predator attacks. We recorded from the DCMD while presenting locusts with looming stimuli that increased or decreased in speed during approach. The change in velocity occurred within a behaviourally-relevant time window. We presented stimuli against simple (white) or flow field backgrounds. Results show that the DCMD responds to a velocity decrease with decreased firing rate approximately 150 ms after transition and the post transition peak is reduced compared to the pre-transition peak. Following transition to a higher velocity, the DCMD response is masked by ongoing firing rate modulation. The presence of a low field consistently reduces DCMD response across stimuli. These results suggest that this motion-sensitive pathway is capable of actively adapting to objects that alter their velocity during approach.
