Mapping neural responses to thermal stimuli in Drosophila larvae

Navigating an environment of temporally and spatially varying stimuli is an important behavior for survival for all motile organisms. The Drosophila larva, an organism with relatively simple brain circuitry, has a robust, quantifiable navigational response to many stimuli, especially temperature. Larvae navigate away from both too-cold and too-warm temperatures. Neurons in the peripheral nervous system strongly respond even to very small decreases and increases in temperature. In the absence of negative or positive stimuli, they explore their environment in a random walk pattern, and respond to sensory stimuli by modulating random walk parameters, particularly turning rate. Our goal is to build a comprehensive map of behavioral and neural responses to variations in temperature. We use reverse correlation to quantify responses to thermal fluctuations, generating probabilistic mathematical filters which describe neural computations in response to temperature changes at a range of offset temperatures. We give temporally varying white noise thermal stimuli to larvae and record behavioral responses, and, separately, responses from individual thermosensory neurons. At the behavioral level, we record and quantify larval navigation, particularly turning events, to generate probabilistic filters which can predict turning rate. At the neuronal level, we record calcium activity to generate probabilistic filters which can predict neuronal activation.