Project Summary / Abstract Our goal is to develop an optical cochlear implant (oCI) that uses photons to stimulate surviving auditory neurons in severely-to-profoundly deaf. The benefit of optical stimulation is its spatial selectivity with the potential to create significantly more independent channels to encode acoustic information and to enhance the CI users’ performance in challenging listening environments and to improve music appreciation. In previous experiments we have defined the parameter space for infrared neural stimulation (INS) in diverse animal models, including the cat. To translate the method into a clinical tool, an opto-electrical cochlear implant, we have to convert the parameter space defined for the cats to the larger cochlea of the humans. In preparation of the study we have communicated with the Food and Drug Administration (FDA) and have submitted a Q- submission for a study risk assessment for the first set of the proposed tests. The purpose of this study is to show that optical and combined opto-electrical stimulation is possible in humans using optical fibers, optical fiber bundles, and a hybrid opto-electrical cochlear implant. Furthermore, the tests will also validate that INS is possible at radiation wavelengths, which are used commercially in communication and for which the technology of optical sources and waveguides is well miniaturized and matured. Most importantly, we will use a forward masking method to validate the view that optical stimulation is spatially more selective than electrical stimulation by comparing the ability of a masking stimulus to reduce the response amplitude of a probe stimulus. Test subjects will be patients with large tumors of the skull base, who require a translabyrinthine craniotomy for tumor removal. For this surgical approach the cochlea and vestibular system will be damaged and the patients will be deaf after surgery. This surgery provides an unique opportunity to test optical stimulation in the human cochlea before it is removed during the tumor resection. Important data can be gathered, which will drive the development of an implantable opto-electrical cochlear implant system by our industrial collaborators. The measurements will take no longer than 30 minutes per patient, after which all the equipment will be removed from the surgical filed and the tumor resection surgery continues.