The ultimate goal of neural science is to understand how interaction between the peripheral and central nervous systems gives rise to human behavior, how sensory information is processed in our brain and memory to stimulate action. But, as human behavior is mediated by a brain with over 100 billion neurons, a comprehensive and integrative approach all the way from sensory input to motor output is currently unimaginable. The fruit fly Drosophila, with sensory modalities, neural circuits, and complex behaviors that are strongly evolutionarily conserved, has emerged as a model system for neural research. Drosophila is simple enough to be tractable, yet complex enough to be scientifically interesting as well as biomedically relevant. This research program will create new paradigms for understanding perception and voluntary action using larval Drosophila, which has unique advantages for this study. In preliminary work, we have used a novel tracking system to quantify the algorithms that underlie larval chemotactic, phototactic, and thermotactic behavior. Using genetic tools provided by our collaborators and new tools that we are developing for optical physiology and behavior quantification in freely moving animals, we will investigate how pathways within the larval brain use information gathered across the larvum?s sensory periphery to make decisions and result in physical behavior. These individual sensory modality studies are the first steps to understanding this model system?s deeper complexities, the behavioral principles and neural encoding behind the brain?s synthesis of the separate environmental representations provided by multiple senses to result in purposeful and coherent behavior.