A central goal of neuroscience is to understand how the brain controls behavior. However, our knowledge of the functional neural circuitry underlying the majority of vertebrate behaviors is incomplete. The larval zebrafish, widely used as a genetic model system, has a diverse behavioral repertoire and a small, transparent brain. This proposal will combine 2-photon laser microscopy and genetically encoded calcium indicators to visualize directly single neuron responses throughout the entire brain of an vertebrate. In Specific Aim 1 we will perform a quantitative analysis of zebrafish visually-guided behaviors in a versatile, custom-made arena. In Specific Aim 2 we will use 2-photon imaging of transgenic fish expressing fluorescent calcium indicators to map responses to behaviorally relevant visual stimuli, identifying individual neurons and circuits that are active during the behaviors described in Aim 1. In Specific Aim 3 we will use targeted laser ablations and analysis of mutants'to test specific hypotheses about the role of individual cellular pathways and neurons in generating behavior. These experiments will map out the functional architecture of the zebrafish brain, revealing sets of neurons that comprise complete behavioral circuits in a vertebrate. Furthermore, they will provide an essential framework for the analysis of neural development, genetic mutants and disease models. PUBLIC HEALTH RELEVANCE: By understanding the basic functional organization of the vertebrate brain we will provide a framework for understanding the behavioral impairments caused by neurological disease. The small transparent brain of the zebrafish makes it possible to visualize the activity of individual neurons, and to study circuits underlying simple behaviors, in models of human disease.