Loom-Sensitive Neurons Link Computation to Action in the Drosophila Visual System

Background: Many animals extract specific cues from rich visual scenes to guide appropriate behaviors. Such cues include visual motion signals produced both by self-movement and by moving objects in the environment. The complexity of these signals requires neural circuits to link particular patterns of motion to specific behavioral responses. Results: Through electrophysiological recordings, we characterize genetically identified neurons in the optic lobe of Drosophila that are specifically tuned to detect motion signals produced by looming objects on a collision course with the fly. Using a genetic manipulation to specifically silence these neurons, we demonstrate that signals from these cells are important for flies to efficiently initiate the loom escape response. Moreover, through targeted expression of channelrhodopsin in these cells, in flies that are blind, we reveal that optogenetic stimulation of these neurons is typically sufficient to elicit escape, even in the absence of any visual stimulus. Conclusions: In this compact nervous system, a small group of neurons that extract a specific visual cue from local motion inputs serve to trigger the ethologically appropriate behavioral response.