Morphology of spiralganglion canal, innervation patterns, and relation to the cochlear scalae: implications for electrostimulation

In the last few decades remarkable advances have been made in comprehending the inner ear morphological structure and the transduction pathways between the external sound signal and the neural substrate. In parallel, cochlear implants have become the most advanced technology in restoring some neurosensory sensations with patient completely deprived of hearing. The population with partially rehabilitated hearing function includes an increasingly large number of children. While much is known and published concerning the organ of Corti, basilar membrane and the hair cells functions, much less is known on the spiral ganglion cells located in Rosenthal`s canal (spiral ganglion canal). The soma of the cells located in the spiral ganglion canal is critical to the electrical stimulation response. A morphological and quantitative analysis of the spiral ganglion canal from base to apex has not been performed beyond the number of cells and cell distribution. As the cochlear implant electrode responsible for conducting small depolarizing currents becomes increasingly refined in design and in positioning, more information is needed on the scala tympani/scala vestibuli/spiral ganglion canal complex. Issues, which need resolution, include: Cross sectional dimensions of the spiral ganglion canal Position of the spiral ganglion canal Bony wall dimensions between the. canal and the scala tympani Role and structure of the nerve bundle arrangement Critical bandwidth of the spiral ganglion canal Fascicular and single nerve organization in the spiral lamina Position and implications of the apical bulge termination of the spiral ganglion Implications and recommendations for the electrode design of cochlear implants The University of Innsbruck, Austria, has been a worldwide pioneer in uncovering the ultra structure of the 8th nerve fibers. A large quantity of previously acquired data is available for review. State of the art equipment is available to collect additional data. Highly qualified researchers are present. Advanced cochlear implant research and development is accomplished in the Innsbruck area. This university is best suited to performing the pioneering work needed to uncover crucial morphological aspects of the inner ear. The uncovered aspects will have profound implication for the design of future generations of cochlear implants electrode arrays.