Patients with severely damaged auditory nerves cannot benefit from cochlear implants. The goal of this project is to accelerate the translation of silicon-based, multisite, penetrating microelectrode arrays to a cochlear nucleus auditory prosthesis. We have recently made significant technological advances with our devices in the cat model, which together with high-count cables and feedthroughs will provide a unique opportunity to develop arrays of multisite microelectrodes that are suitable for clinical use. This project will demonstrate the feasibility of interfacing a multisite microelectrode array with a lare number of microstimualting sites to an implantable pulse generator (IPG), in preparation for a subsequent clinical trial. Validation of the cochlear nucleus implant for clinical use will also advance other configurations of silicon- substrate multisite microelectrode arrays toward clinical use. These include the auditory nerve and the auditory midbrain (inferior colliculus), and perhaps even the primary auditory cortex. We are proposing to conduct appropriate tests under two ISO (International Organization for Standardization) guidelines: (1) ISO 10933 in Aim 1 to validate the biocompatibility of the electrode array and associated cables, and (2) ISO 14708 in Aim 2 for interfacing the array and cable to a neurostimulator. In Aim 2, we will develop the interface to an IPG, and determine the compliance of the system in-vitro per ISO 14708 which specifies requirements for reliable interfaces to neurostimulators. These tests are a critical majo step to optimizing our devices for a future investigational device exemption by the FDA. The successful outcome of the project will be the translation of a new generation of multisite, penetrating silicon microelectrode arrays that will be implanted in a human cochlear nucleus, allowing for unprecedented access to the tonotopic organization of the nucleus. Finally, these multisite silicon devices can be modified for other neurological conditions including spinal cord and deep brain stimulation.