INFORMATION PROCESSING IN LAMINATED NEURONAL NETWORKS

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We intend to continue our studies on sensory information processing and the control of simple behavioral responses in electric fish. We have chosen the electric sense as a model system for the exploration of basic neuronal design features which also appear to be involved in more complex sensory systems, such as audition and vision in mammals. Of particular interest are ordered representations of stimulus spaces in laminated neuronal networks which map certain stimulus variables along particular axes within the plane of lamination and process different aspects of the stimulus complexity by specialized neurons located in different layers. By advancing through successively higher-order central nervous stations of stimulus processing, we intend to reach the motor output level and thus to provide a complete neuronal theory for the control of a simple behavioral response. For the Jamming Avoidance Response in Eigenmannia, this goal is now within reach. This proposal focuses upon three projects: 1. The significance of representations of afferent information in multiple maps, such as the projections of identical primary electrosensory afferents to three separate, somatotopically ordered maps in the hindbrain. This research involves intracellular recording and labelling of all available cell types to study their dynamic properties under various stimulus regimes and their anatomical architecture. Differences between the three maps should yield clues for their functional specialization. 2. The significance of descending recurrent input from midbrain and cerebellum to all three electrosensory maps in the hindbrain. The effects of small lesions upon dynamic properties of identified cell types as well as upon responses of the whole animal will be studied. 3. The organization of the medullary electric organ pacemaker. Although not a strictly laminated structure, this nucleus consists of two loosely segregated types of electrically coupled, rhythmically discharging cells which control the electric organ. To investigate causes for the extreme stability of its rhythm, physiological experiments will be conducted on intact preparations, on excised pacemakers maintained in a slice chamber and on pacemaker cells grown in tissue culture. These studies will involve dual intracellular recording and labelling of coupled cells and anatomical investigation of their connections.