Function and Plasticity in a Mapped Sensory System

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Within the brain, sensory systems often show an spatial mapping of sensory stimulus properties. In such a "map" an array of neighboring nerve cells shows a systematic variation in the responsiveness, or "tuning", of each cell to some particular sensory parameter, such as the pitch of a sound or the orientation of a visual bar. It is not yet understood just how such highly specific maps develop, nor how that development may depend on experience. This project uses a part of a relatively simple insect nervous system that has physiologically characterized and individually identifiable neurons. The cricket has a pair of sensory appendages, called cerci, at its rear end. Each cercus is very sensitive to airborne sounds and vibrations, and sends sensory signals to a central ganglion where interneurons initiate appropriate motor behavior such as escape. Extracellular and intracellular recordings and dye-filling will be used with sophisticated confocal microscopy and computer reconstruction of the incoming afferent projections, their synaptic sites, and the morphology of the target interneurons. An anatomical map will be constructed using projections of single neurons that encode wind velocity and wind direction. This map predicts where activity should occur in the system for a particular stimulus, and will be tested by activity-dependent dyes during physiological tests. The objective is to describe the structural and functional organization of this well-defined, topographically mapped sensory system. The development of this map will be traced from younger tages, to compare to the adult map, and to see whether functional changes occur during development. Results from this novel approach will have impact on many areas of sensory and developmental neuroscience, by clarifying the cellular mechanisms of this widespread mapping principle.