1Animals rely on multiple sensory information systems to make decisions. The integration of 1 2 information stemming from these systems is believed to result in a precise behavioural 1 3output. To what degree a single sensory system may override the others is unknown.
4Evidence for a hierarchical use of different systems to guide navigation is lacking. We 1 5used Drosophila melanogaster to investigate whether, in order to relieve an unpleasant 1 6 stimulation, fruit flies employed an idiothetically-based local search strategy before making 1 7 use of visual information, or viceversa. Fruit flies appear to initially resort to idiothetic 1 8 information and only later, if the first strategy proves unsuccessful to relieve the 1 9 unpleasant stimulation, make use of other information, such as visual cues. By leveraging 2 0 on this innate preference for a hierarchical use of one strategy over another, we believe 2 1 that in vivo recordings of brain activity during the navigation of fruit flies could provide 2 2 mechanistic insights into how simultaneous information from multiple sensory modalities is 2 3 evaluated, integrated, and motor responses elicited, thus shedding new light on the neural 2 4 basis of decision-making. 2 5 3 1 the knowledge of the relationships between different sensory information systems, and 3 2how animals use these to reach their goals is just at its beginning [15][16][17]. To the best of 3 3 our knowledge, there is no evidence for a hierarchical use of different information systems 3 4 to guide navigation in simple animal models [18]. Invertebrates, particularly insects, are 3 5 excellent models to study how a less complex brain produces behaviours [19,20]. Insects 3 6 can be trained to pinpoint a location in space where an unpleasant stimulation ceases, 3 7where food may be present, or where a pleasant sensation may be experienced [2,21-23]. 3 8 Insects explore their environment while relying on multiple sources of information, of which 3 9 the most studied are visual cues and path integration. Visual stimuli can be associated 4 0 with a stimulus of relevance to the animal, and having a positive valence, such as the 4 1 obtainment of food, the relief from a negative stimulus or the possibility of mating. Path 4 2integration is the behavioural output of an "internal pacemaker", the activity of which 4 3 guides the locomotion of the animal in order to maximize its chance of reaching a relevant 4 4 stimulus previously encountered while navigating. We used Drosophila melanogaster to 4 5 investigate whether we could find evidence for the hierarchical use of different sources of 4 6 information; specifically, we asked the question whether, in order to relieve an unpleasant 4 7 stimulation, fruit flies employed an idiothetically-based local search strategy before making 4 8 use of visual information, or viceversa. 4 9 3 2 8 mean and the confidence interval around the mean. A) Mean number of fruit flies, which 3 2 9are initially outside both zones and that at the onset of optogenetic stimulation (at...
