Peripheral Neural Coding Strategies for Spectral Analysis and Sound Source Location in a Non-teleost Bony Fish, Acipenser Fulvescens

Title of Dissertation: PERIPHERAL NEURAL CODING STRATEGIES FOR SPECTRAL ANALYSIS AND SOUND SOURCE LOCATION IN THE NON-TELEOST BONY FISH, ACIPENSER FULVESCENS Michaela Meyer, Doctor of Philosophy, 2008 Directed By: Professor Arthur N. Popper, Department of Biology, University of Maryland, CP and Professor Richard R. Fay, Parmly Hearing Institute, Loyola University of Chicago This work is an investigation of coding strategies for spectral analysis and sound source location in Acipenser fulvescens, the lake sturgeon. A. fulvescens belongs to one of the few extant non-teleost ray-finned fishes. The sturgeon taxonomic family, the (Acipenseridae), has a phylogenetic history that dates back about 200 million years. Studies on sensory coding in any species of this family or any other non-teleost species have not been conducted before. Thus, this is the first study on peripheral coding strategies by the auditory system in a non-teleost bony fish. For this study, a shaker system, similar to that used in previous experiments on teleosts, was used to simulate particle motion of sound at the ears and auditory periphery of A. fulvescens. Simultaneously, electrophysiological recordings of isolated single units from the eighth nerve were obtained. Peripheral coding strategies for spectral analysis and sound source location in A. fulvescens resembled those found in teleosts. Frequency data resembled the characteristics found for auditory afferents (with preferences for lower frequencies) in land vertebrates. In addition, the auditory periphery in A. fulvescens appears to be well suited to encode the intensity of sound. In terms of mechanisms for sound source location, eighth nerve afferents responded to directional stimuli in a cosine-like manner (as in teleosts), which can generally serve as the basis for coding the location of a sound source. Certain differences to teleosts were also found in A. fulvescens and these may have implications for the mechanisms for sound source location in azimuth. The common physiological characteristics between A. fulvescens, teleosts, and land vertebrates may reflect important functions (that are part of the process of auditory scene analysis) of the auditory system that have been conserved throughout the evolution of vertebrates. PERIPHERAL NEURAL CODING STRATEGIES FOR SPECTRAL ANALYSIS AND SOUND SOURCE LOCATION IN THE NON-TELEOST BONY FISH, ACIPENSER FULVESCENS.