Infrared Laser Stimulation of Cochlear Nerve through a Tympanic Membrane

Abstract

Infrared lasers are a novel method for providing neural stimulation. The laser causes an instantiable temperature rise because of optical absorption by water, and opens the heat-sensitive ion channel. Unlike electric stimulation, an infrared laser stimulates nerves without contacting the tissue. Our goal was to develop a novel auditory prosthesis by applying infrared laser stimulation in a hearing aid. This study investigated whether an infrared laser projected through the tympanic membrane could stimulate the cochlear nerves in the ear canal. Mongolian gerbils (Meriones unguiculatus) were studied. A pulsed infrared laser (0.5-12.8 mJ/cm2) and a clicking sound (10–90 dB pe. SPL) were presented to the subjects. The cochlear microphonics (CMs) and compound action potentials (CAPs) were recorded when the clicking sound was presented, while trans-tympanic membrane laser stimulation induced only CAPs. In subsequent experiments, continuous pulsed laser irradiation for 60 minutes did not cause any observable damage on cochlear response and a tympanic membrane. Therefore, trans-tympanic membrane laser stimulation bypasses the need for hair cell depolarization and creates cochlear nerves responses directly, suggesting that a novel hearing aid using an infrared laser could compensate for sensorial hearing loss.