RET subproject for Reticulospinal Execution of Innate Decision-Making

This proposal outlines research to investigate the neural and mechanical bases of innate decision-making in vertebrates. It will use larval zebrafish (Danio rerio), not only because of this organism's simplicity and great accessibility to an array of investigative methods, but also because larval zebrafish undergo a discrete change in their innate decision-making ability during the first few days after hatching. Immediately after hatching, larval zebrafish have the ability to generate escape behavior in response to threats. Three days later, they add to this repertoire the ability to approach and then attack small objects detected visually. How is the neural circuitry supporting the escape movement, with large amplitude body bends away from the stimulus, modified or supplemented in order to obtain precise, small amplitude body bends toward the stimulus? The investigation will pursue several hypotheses using high-speed videography and automatic body tracking, calcium imaging, in-vivo physiology, and advanced computational fluids and body-modeling methods. Predation of mobile animals by other mobile animals may have been central to the very emergence of nervous systems. The most ancient need of the stem bilaterians in which carnivory likely originated is the ability to not only turn away from threats, which likely originated prior to the invention of carnivory, but to turn toward moving opportunities, such as another animal that could be eaten. Whether to turn away or to turn toward is the most fundamental decision an animal can make, and relies upon coordinated activity across multiple levels of the nervous system. While it occurs in all predators, its early appearance in larval zebrafish, just 72 hours after hatching in a transparent nervous system consisting of only 100,000 neurons, presents a great opportunity for understanding how complex neural and mechanical systems are supplemented or modified to provide a discrete switch from the coarse and rapid movement features of escape to the fine and slow movement features of predatory approach. Over the past decade a significant amount of understanding of the spinal circuitry underlying fast and slow movements of the larval zebrafish has accumulated. How descending systems may make use of these patterns to execute appropriate behaviors is still unclear. The proposed work will bridge this gap using new and innovative work by the PIs on prey capture behavior and methods for generating prey approach and predator avoidance behaviors in head-fixed animals. These will be used to address the circuit mechanisms of this primordial innate decision. High fidelity models of the body and swimming will complement behavioral, imaging, physiological and genetic techniques to inform how the decision is distributed across levels of the nervous system and the mechanics of the body in interaction with the surrounding fluid. The team has a record of commitment to novel outreach efforts, including Science Cafes, interactive science-inspired art installations, large scale public events such as TED talks, and advising leading movie and TV show creators on how to improve the quality of science depicted in their work. For this proposal, the group will collaborate with teachers from a local high school to develop a unit for Advanced Placement Biology students in which students will learn how to devise very simple robots that demonstrate basic behaviors motivated by the proposed research. We envisage a sequence of robots in which the first level of challenge will be to devise a robot with only two light se