Striking parallels in the anatomical organization of medullary nuclei in the lateral line and electrosensory system of fish and in the vertebrate auditory systems suggest that there may be some fundamental principles of organization and cellular interactions that apply to all three systems. The long term objective of this research is to increase our understanding of the functional significance of this organization in a comparative and evolutionary context, particularly with regard to how spatially-mapped patterns of stimulus amplitude are processed by brainstem medullary nuclei in vertebrate hair cell systems. Since the lateral line system of fish consists of a spatial array of hair cell receptors, superficially located ont he body of the fish, it is ideally suited for investigations on the encoding of spatial patterns. A series of anatomical, behavioral and physiological experiments will be conducted on two teleost fish species. Anatomical techniques will be used to determine the cytoarchitecture and organization of the lateral line medullary nucleus and the extent to which this nucleus is similar to electrosensory and auditory brainstem nucleii. Behavioral techniques will be used to measure the ability of fish to use their lateral line system to detect different spatial flow patterns created by moving objects in stagnant water and by stationary objects in water currents. These stimuli approximate the kinds of stimuli, such as moving prey or obstacles in a stream, naturally encountered by fish in their environment. Neurophysiological techniques will be used to measure the responses of single primary afferent and secondary medullary fibers to the same stimuli. Response properties from peripheral fibers will be compared to those of medullary fibers to determine what transformations are occurring in the medullary nucleus. Finally, behaviorally measured abilities will be compared to physiologically-measured response properties to determine how spatially complex signals are encoded and processed at different levels of the nervous system.