Project Summary The central goal of this project is to advance the therapeutic application and the development of an exciting novel neuroprosthetic technology, Safe Direct Current Stimulation (SDCS). Direct current (DC) compared to biphasic charge balanced pulses normally used by neural prostheses to interface to the nervous system, can more naturally control neural activity. Unlike biphasic current pulses used to excite neurons, DC can excite, inhibit, and modulate sensitivity of neurons. However using DC for implantable prosthetic applications has not been possible due to the DC’s inherent violation of the charge injection safety constraints at the metal electrode interfaces. Safe DC overcomes these constraints and opens a new avenue for research into exciting possibilities of using DC to interface to the nervous system. We will optimize the use of SDCS to improve the performance of the vestibular prosthetic for balance disorders. This type of neural implant is designed to deliver the sensation of head motion directly to the vestibular nerve for those suffering from bilateral vestibular dysfunction. We obtained preliminary data in a chinchilla animal model showing that using DC in contrast to the more conventional pulsatile stimulation can dramatically increase the range of head velocities that can be encoded by the device. Here we propose to consider biological safety of long-duration SDCS prosthetic stimulation, and advance the technology SDCS toward primate implantation. Aim 1) Conduct acute behavioral studies in nonhuman primates. Aim 2) Determine whether prolonged DC delivery from the SDCS causes physiologic or histologic signs of damage in chinchillas. Aim 3) Develop a three channel SDCS, lead, and DCtubes designed for future primate chronic vestibular implant studies.