Effects of semicircular canal electrode implantation on hearing in chinchillas

Conclusion. Implantation of vestibular prosthesis electrodes in chinchilla semicircular canal ampullae can be accomplished without significant loss of cochlear function; however, the risk of hearing loss with the current surgical technique is high. Objectives. To determine if it is possible to implant vestibular prosthesis electrodes into the labyrinth without damaging hearing, and to quantify the extent of hearing loss due to implantation. Materials and methods. The left semicircular canals of six chinchillas were implanted with three bipolar pairs of electrodes using a transmastoid approach. Right ears, which served as controls, were subjected to the same mastoid approach without fenestration and implantation. Auditory brainstem response hearing thresholds to free-field clicks and tone pips at 2, 4, 6, and 8 kHz were measured bilaterally 3-9 weeks after implantation. Hearing thresholds were compared between sides and against data from six normal chinchillas. Results. Four implanted ears suffered severe hearing loss, with thresholds ranging from 5 to 11 SD above the mean threshold of sham surgery control ears across all tested stimuli. Two implanted ears had preserved hearing, with thresholds remaining within 1 SD of the mean threshold of sham surgery control ears across nearly all stimulus frequencies.