Dragonfly target-detecting neurons adapt to stimulus saliency

The dragonfly visual system contains neurons that respond to the movement of small targets, even when embedded in visual clutter. Some of these target-detecting neurons facilitate their spiking activity to targets moving along continuous trajectories and selectively attend to one target when presented in a pair. When a target is rapidly repeated, the spiking activity of these 'small target motion detector' (STMD) neurons decreases. This 'adaptation' is spatially localised with a time course dependent on the frequency of stimulation. Here, we presented rapidly repeating targets of varying contrast and direction, as well as perturbing facilitatory and selective pathways by evoking localised adaptation. Using extracellular electrophysiology, we show that higher target contrast elicits stronger adaptation; however, the time course of diminishing responses was similar across contrasts. This relationship between target saliency and adaptation is also observed with targets moving in the preferred direction causing stronger adaptation. Targets that jitter, as is likely the case during rapid head foveation of prey, induce less adaptation as the jitter radius increases. We observed that the strengthening effect of facilitation competes against suppressive adaptation. Moreover, we observed that STMDs are unlikely to selectively attend to targets that traverse an adapted location. These results provide insight into how dragonfly target-detecting neurons adapt their responsiveness to visual targets in their environment that would be encountered during flight when pursuing prey or conspecifics.