Active sensation during orientation behavior in the Drosophila larva: more sense than luck

The fruit fly Drosophila larva demonstrates a sophisticated repertoire of behavior under the control of a numerically simple neural system. Historically, the stereotyped responses of larvae to light and odors captivated the attention of biologists. More recently, the sensory receptors responsible for chemosensation, thermosensation, and vision have been identified. While our understanding of the molecular logic of perception has clearly progressed, little is known about the neural and computational mechanisms guiding movement in sensory gradients. Here we review evidence that larvae orient based on active sensation - a feature distinct from the strategies used by simpler model organisms. Reorientation maneuvers are controlled by the spatiotemporal integration of changes in stimulus intensity detected during runs and lateral head movements.