Vestibular Co-stimulation in Adults with a Cochlear Implant

Background : Vestibular co-stimulation is a side effect of cochlear implant stimulation. The electrical currents delivered by the cochlear implant can spread toward the vestibular system and thus stimulate it. The aim of the study is to evaluate whether it is feasible to functionally restore the balance by modifying the vestibular co-stimulation. Methods: Four adult patients, who had received a commercially available cochlear implant previously, were enrolled. Counterbalanced biphasic pulses were presented as bursts or as an amplitude-modulated biphasic pulse train (modulation frequencies ranging from 1 to 500 Hz) at the participant’s upper comfortable level for electrical stimulation. Subjective sensations and vestibular-mediated eye movements were used for evaluating the possible effects of vestibular co-stimulation. Results: One participant experienced a cyclic tilting of his head in response to an amplitude-modulated biphasic pulse train with a modulation frequency of 2 and 400 Hz. However, during a follow-up visit, the sensation could not be replicated. Conclusion: Subjective vestibular sensations or vestibular-mediated eye movements could not be electrically evoked with a commercially available cochlear implant in 4 adult patients with almost normal vestibular function. Therefore, customized design of the hard-, firm-, and/or software of the commercially available cochlear implant might be necessary in order to electrically restore vestibular performance.