Prof. Doug Fitzpatrick
Otolaryngology / Head and Neck Surgery, UNC School of Medicine, USA
Since 2008 I have been involved in a project to physiologically monitor cochlear responses to sound before, during and after cochlear implantation. The project was begun by Drs. Oliver Adunka and Craig Buchman, who are Neurotologists who came to me with the idea that this monitoring strategy could be used to reduce trauma to help preserve residual hearing and improve speech perception outcomes with the implant. They had already done some proof-of-concept recordings in humans but came to me, a neurophysiologist studying the auditory system in animal models, to do some studies in animals to help identify appropriate stimuli and biomarkers of trauma based on insertions of electrodes into the cochlea. After a series of successful experiments in both normal-hearing gerbils and gerbils with noise-induced hearing loss, we returned to intraoperative human recordings. Since then we have obtained ECochG results from the round window and/or within the cochlea in more than 300 adult and pediatric implant subjects. In addition to the original idea of monitoring to measure and possibly reduce trauma, we found that the residual function in CI subjects accounts for a large amount (40-50%) of the variability in speech perception outcomes in quiet commonly seen in CI subjects. This is an unprecedented degree of correlation with speech perception outcomes, much greater than any other factor such as age or duration of deafness seen in the modern implant population. Finally, we have continued parallel pharmacological experiments in animals to better understand the ECochG response, which is complex mixture of components derived from hair cell and neural sources.