INPUT/OUTPUT PROPERTIES OF A MAPPED SENSORY SYSTEM

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The goal of this research project is to determine how a relatively complex sensory system extracts and encodes information from external stimuli. The response properties of the system will be observed and characterized at two levels: at the receptor level and at the output layer to higher CNS levels. During some experiments, the responses from all of the cells in the output layer will be monitored simultaneously. Analysis of this data will provide a complete description of the input/output properties and encoding algorithm of this system. The preparation to be studied is the cercal sensory system of the cricket, Acheta domesticus. Crickets (and many other insects) have two antenna-like appendages at the rear of their abdomen, covered with hundreds of "filiform" hairs, resembling bristles on a bottle brush. Deflection of these filiform hairs by wind currents activates mechanosensory receptors, which project into the terminal abdominal ganglion to form a topographic representation (or "map") of "wind space". Primary sensory interneurons having dendritic branches within this afferent map of wind space are selectively activated by wind stimuli with "relevant" parameters, and generate action potentials at frequencies that depend upon the value of those parameters. The "relevant" parameters are thought to be the direction, velocity, and acceleration of wind currents directed at the animal. There are only ten pairs of these interneuons which carry the system's output to higher centers. All ten of these output units are identified, and all will be monitored simultaneously with extracellular electrodes. The following specific questions will be addressed: What are the response properties of th sensory receptors, and what are the I/O properties of the receptor layer as a whole? What are the response properties of all the units in the output layer? Is all of the direction, velocity and acceleration information that is extracted at the receptor layer also available at the output layer? How is that information encoded? Are any higher order "features" also encoded? What is the overall threshold, sensitivity and dynamic range of the system as a whole for detecting features of wind stimuli? An attempt will be made to assess how all of the observed properties relate to the structure of the output neurons, the synaptic connectivity of the output interneurons with other local interneurons, and the synaptic connectivity of the output neurons with the sensory afferents in the map of wind space.