9320362 Brownell Chemosensory pathways in the central nervous system of animals generally lack the topographic organization commonly found in the visual, auditory and somatosensory systems. A remarkable exception to this generalization has been discovered in chemosensory appendages called pectines of nocturnal sand scorpions. These pectines contain an array involving roughly a million chemosensory neurons, which "map" in a precise spatial organization into a discrete part of the central nervous system. This project uses chemistry, electrophysiology, anatomy and behavior to determine the chemical stimulus compounds that are deposited by these animals as they walk (apparently used for tracking by others), to determine how interactions between primary peripheral neurons can shape the sensory response to particular chemicals, and to determine the precision of topographic order in the central map from individual sensory afferent fibers. The results will help understand the physical characteristics of substrate-associated chemosensory signals and how chemosensory systems are specialized for that role rather than for airborne or water-borne chemicals. The use of an arthropod considered to represent a primitive group will lead to insights about the evolution of chemosensory sytems found in more derived arthropods such as crustaceans and insects. Results also will have an impact on our understanding of how sensory neural systems in general utilize topographic maps for sensory information processing. ***
