Laser stimulation of the auditory nerve

BACKGROUND AND OBJECTIVES: For centuries, electric current has been used to stimulate neurons. Shortcomings of electrical stimulation include the contact between the stimulating electrode and the tissue, and the non-selective stimulation of the tissue. In contrast to electric stimulation, optical radiation can provide spatially selective neural stimulation without tissue contact. STUDY DESIGN/MATERIALS AND METHODS: Acute in vivo experiments using gerbils were conducted to record optically evoked compound action potentials (CAPs) from the cochlea. RESULTS: Optical radiation evokes CAPs in normal hearing animals and in deafened animals, in which cochleae lack outer and inner hair cells. Stimulation threshold was measured as 0.018+/-0.003 J/cm(2) (mean+/-SE). Laser radiation could be increased by 30-40 dB until drastic changes were seen in cochlear function. Cochlear response amplitudes to optical radiation were stable over extended stimulation times. CONCLUSIONS: We have demonstrated that the auditory nerve can be stimulated by optical radiation. One potential clinical use of this technology would be for cochlear implants.