Cochlear Implantation Feasibility in Rhesus Macaque Monkey

BACKGROUND: Large animal models of implantable hearing devices are needed to assess innovative technologies before using them in humans. The rhesus macaque has cognitive abilities close to humans and has been used in the past but with noncommercial implants or no detailed radiologic descriptions of the surgical procedures. The aim of this study was to evaluate the feasibility of cochlear implantation in this animal model. METHODS: We present detailed radiologic data (CT scan and Cone beam computed tomography) from 7 heads of rhesus macaque monkeys coming from autopsy materials. Several comparative measurements were performed with 10 human temporal bones to emphasize similarities and differences between the macaque and the human inner ear. The radiologic analyses helped planning the surgical approach for cochlear implant insertion in the macaque. RESULTS: We managed to perform one full (720 degrees) and 3 partial insertions (190-330 degrees) of cochlear implants in 4 rhesus macaque cochleae, documented by cone beam computed tomography reconstructions. We confirm that the procedure is facilitated in this animal because the cochlea dimensions are close to humans. However, marked differences in the orientation of the external auditory canal and the basal turn must be taken into account. We suggest that the removal of the inferior wall of tympanal bone provides the optimal axis for electrode array insertion. CONCLUSION: The rhesus macaque monkey is a valid and close-to-human animal model for cochlear implants insertion. Because this species is widely used in both behavioral and physiologic studies, we expect that functional implants can be coupled with electrophysiologic recordings to study the mechanisms of auditory compensation.