Visual evidence accumulation in Drosophila melanogaster

In a complex and mutable environment, animals continuously face scenarios where behavioral decisions determine their survival. These rely primarily on sensory input and the associated cognitive process is known as perceptual decision-making. The decision-making is typically preceded by the gathering of information across time in a process called evidence accumulation. This has been widely studied on various animals; however, in flies, the emphasis has primarily been centered on the subcellular integration mechanisms, overlooking the behavioral impacts and whole-brain neuronal dynamics.Here, we investigated, from a behavioral perspective, how tethered flies engage in perceptual decision-making during a two-alternative choices paradigm based on visual input. In this test, subjects are required to make a motor choice based on the effective valence of the visual stimulation. From the tracking of the head movements, we extracted the saccades features as function of the relative valence of the visual stimulation. Our results highlight stereotyped dynamics of the identified saccades. As expected, greater valences lead to an increase of the total saccades number and an increase in the proportion of correct outcomes with respect to the sensory stimulation. Moreover, results suggest that valence impacts on the timing of the correct movements: higher is the valence, shorter is the time for the emergence of the correct movements. This suggests that the underlying circuits operate like an integrator, as shown in other model organisms. In conclusion, we behaviorally identified an evidence accumulation mechanism that will allow us to investigate the underlying neuronal processes.