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Publications in VIVO

Ketten, Darlene Emeritus Research Scholar, Biology


My work is divided between the practical and theoretical. On the practical side, much of my work involves postmortem examinations of strandings to determine cause of death and documentation of pathologies, particularly those related to head and neck traumas and blast injury. On the theoretical or basic research side, I focus on understanding how ear structures that vary by species relate to differences in hearing abilities. These two areas cross-pollinate; the basic research helps us to understand how changes in an ear, brought about by disease, are markers for specific forms of hearing loss, and my work with human ears and cases gives invaluable training for better determinations of head and neck pathology in other vertebrates. My basic, comparative species research concentrates on how animals, like bats, elephants, and whales, with exceptional hearing capacities achieve acute infra and ultrasonic hearing. The most important recent result from this work is the development of a mathematical model relating cochlear topography to the preservation of low frequency hearing despite the limitations placed on LF penetration via the middle ear and how soft tissues in dolphins heads evolved to play a role in underwater sound reception. This fundamental research on mechanisms also examines normal vs. hearing impaired ears to determine how location and nature of pathologies that impair hearing relate to specific changes in frequency and intensity perceptions. For both research areas, the data are obtained from three-dimensional computerized models of the inner ear produced from histological sections and computerized tomographic images (CT and MRI scans). More recently, I have also added Atomic Force Microscopy to the techniques employed in order to directly address variations in membrane stiffness both longitudinally within individual cochleae and across species. The mapping and ultrahigh resolution CT techniques developed in the basic animal research have become valuable tools in the human studies as well, particularly for cochlear implant and blast trauma research. The techniques develop the exceptionally dense dolphin head structures are now used to map the position in vivo of intracochlear abnormalities pre-operatively and the location of each electrode in individual implant patients post-operatively. Current studies are focusing on the relationship of electrode position to speech perception and on mechanisms of insertion trauma. Results to date show significant inter-individual variation in array insertion depths and that the array in most patients impacts the cochlear wall in the mid-basal turn, primarily because the average curvature of the human ear is tighter than the curvature the array “naturally” pursues based on its stiffness. Impacts and intra-canal obstructions cause compression or torsion of the array that are identifiable and can be monitored in vivo. These sites are strongly correlated with deficient electrode performance. While the imaging methods and data on patient differences have already had some impact on surgical planning, the greatest benefit from this research will likely be, in the long term, to foster improvements in cochlear implant designs and to provide intraoperative techniques for optimizing array placement in every patient. Most recently, these studies have also provided algorithms for imaging and measuring pathologies that have since been applied to a range of head and neck traumas and abnormalities, particularly volumetric differences in traumatic brain injury cases and fine grain analyses of blast injury and fragment and shrapnel patterns.

selected publications