Although the cochlear implant is among the most successful of neural prostheses, there remains extreme variability in hearing results enjoyed by implant recipients. Thus open set word recognition scores vary between 0% and over 95%. In addition, the immediate and delayed trauma induced by cochlear implantation is extremely variable and in some cases may be progressive and lead to worsening of the word recognition scores achieved postoperatively. The overall objectives of the proposed research in this grant application are (1) to predict and maximize the word recognition scores in patients who have undergone implantation and (2) to limit the immediate and delayed trauma to the inner ear after cochlear implantation. All of the specific Aims are directed toward one or both of these objectives: Aim 1. Develop, test, and implement patient-specific electro-anatomic models (PSEAMs) and use to identify peripheral anatomic and physiologic factors that limit performance as judged by word recognition scores (overall objective 1). Aim 2. Perform a correlation study between histologic and radiographic reconstruction of intracochlear electrode position in postmortem human temporal bones (overall objectives 1,2). Aim 3. Evaluate the preservation of supporting cells of the organ of Corti as possible candidates as progenitor cells in future regenerative therapy following cochlear implantation in the human (overall objective 2). This Aim will be facilitated greatly by the successful accomplishment of Aim 2, which will allow improved histologic and immunohistochemical studies of these human specimens. Aim 4. Characterize the cellular immune response to cochlear implantation in the human using lymphoid cell markers for T and B cell subsets (overall objective 2). More than 50% of human specimens from patients who in life have received a cochlear implant demonstrate some evidence of cellular immune response which may cause postoperative degenerative changes including fibrosis, new bone formation and cellular loss which may limit the capacity of regenerative techniques. Better characterization of this cellular immune response may provide opportunity for prevention or medical intervention. Aim 5. Evaluate the histopathologic changes in temporal bones from humans with otosclerosis and cochlear implantation (overall objectives 1 and 2). Otosclerosis is extremely common in the human population (approximately 1 in 10 individuals) and has been well documented to cause incomplete or aberrant insertion of electrodes in some cases, and may require alteration of the stimulus strategy. Aim 6 (formerly Aim 7). Continue the accrual of well documented human temporal bones from patients who in life had undergone cochlear implantation (overall objectives 1 and 2).