Project 2 It is the behavioral algorithms that dictate the questions and framework for any model of neural implementation. Thus, to discover how behavioral algorithms are implemented and to generate a realistic brain-body circuit model for larval zebrafish, we need, in addition to knowledge about the anatomical structure of the circuits, detailed information about neural activity patterns during behavior. Further, behavioral algorithms must be implemented in the context of the embodied animal, which is subject to physiological demands, fluctuations and constraints. In order to accommodate both of these requirements, we will estimate and incorporate these physiological state variables into our modeling framework. In order to obtain the necessary datasets, we propose to add detailed measurements of heart and gills, as well as body wide recordings from the autonomic nervous system (ANS) and the intrinsic cardiac nervous system (ICNS) to our experimental repertoire. Such recordings will be combined with established brain wide imaging technologies, where we will focus on critical regions, such as the hypothalamus and various other areas that were already identified to play an important role in the modulation of behaviors and internal states. To facilitate the quantification and control of state-dependent variability, we have also designed a set of behavioral assays where environmental context is modulated to induce specific changes in the animal's internal and autonomic state. The comprehensive data sets collected in these experiments then allow for the generation of a family of realistic circuit models that could, in principle, implement the behavioral algorithms and that can reproduce and emulate the recorded neural and cardiac activity patterns. These realistic models allow for the generation of specific predictions and hypotheses about many of the unconstrained parameters in the underlying circuits. Such parameters include specific connectivity patterns, the synaptic weights, the excitability of membranes and many more. In order to constrain this large variety of variables one needs to apply a variety of independent approaches. To that end we will take advantage of the extensive experimental toolset already developed in the context of the current U19 grant, which includes the use of optogenetics based circuit interrogation, targeted electrophysiology and sparse connectomics tracing in overlaid EM volumes. Many of these experimental approaches require tethered behavioral preparations which are already established in our laboratories. Such preparations provide the ideal setting for brain wide imaging and targeted perturbation, and they will therefore facilitate the generation of a further refined set of validated circuit models for our various behavioral assays. To summarize, our goal is to first validate and constrain a set of realistic circuit models that we have already generated in the context of the current U19, to integrate these validated mod...