Neural Control of Steering in Walking Drosophila

Abstract

Steering is a fundamental component of orienting behavior. It can be guided by external sensory cues, internal drives, and goal directions stored in working memory. Steering behavior provides an opportunity to study how the brain toggles between these different drives with different goals. It also provides an opportunity to study how the brain combines steering guidance information from multiple sensory modalities with steering guidance information in working memory. How sensory cues and internal cognitive drives are integrated to guide motor commands is a major open problem. In this study we made significant progress toward solving this problem by identifying two types of descending neurons (a1 and a2) that influence steering during walking in Drosophila. Whereas a1 acts in a sustained manner with low gain, and a2 acts transiently with high gain. We showed that a2 responds to spatial guidance cues with different valences from multiple stimulus modalities. These neurons encode the direction of the cue evoked turn, not the side of the body where the cue was delivered. Moreover, we showed that a2 is functionally downstream from the heading direction map in the central complex, and it can participate in steering behavior driven by central complex dynamics. Finally, we suggest future strategies for examining the mechanism of integration between central complex-related inputs and sensory-related inputs onto steering descending neurons.