NEURONAL STRUCTURE AND FUNCTION IN A SENSORY PROCESSOR

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Due to its relative simplicity, the electrosensory system is ideally suited for the integration of behavioral and cellular approaches and, therefore, has led to most detailed explanations of stimulus perception and motor performance at the single-cell level. The electric sense shares basic principles in the coding of sensory information with more advanced sensory modalities, such as vision and audition in birds and mammals, and thus provides a convenient model system for studying neuronal mechanisms of information processing in general. Most significantly, some behavioral responses of electric fish are so robust that they remain intact in physiological preparations, thus allowing simultaneous studies at the behavioral and cellular level. The current project will continue to explore the structural and functional organization of the torus semicircularis, a laminated midbrain structure homologous to the inferior colliculus of mammals, which processes temporal and spatial aspects of electrosensory information. By using quartz glass pipettes (prepared by the new 'laser puller' of the Sutter Company), even very small cells, with soma diameters in the range of 5 micra, can now be penetrated and labelled intracellularly. This offers the opportunity of labelling and recording from neurons that could barely be explored in the past. One of these small-neuron types resides in lamina 6 of the torus and computes temporal disparities in the arrival of two inputs, comparable to the processing of interaural time differences in auditory systems. The temporal resolution of these neurons appears to be in the microsecond range. In addition to studies in largely intact fish, we intend to explore functional and structural properties of the torus in slice preparations. Due to the anatomical organization of projections to the torus, one could stimulate lamina 6 of the torus in a near natural manner and explore the physiological properties of small cells under the enhanced mechanical stability of a slice preparation.