How does cochlear implantation affect the contralateral vestibular system?

Cochlear implantation has been performed for 16 years by investigators at Semmelweis University. During this period, different types of cochlear implants have been used and, in 30% of cases, hearing was observed to be restored in the nonimplanted ear. In addition to contralateral hearing improvement, significant improvement was observed in the caloric responsiveness of the nonoperated labyrinth. The preoperative median value of the average slow-phase velocity of the caloric test increased, and the increase was statistically significant on the contralateral side. The reason for this caloric response improvement is unclear, although possible explanations are brain plasticity or presently obscure trophic influence on the vestibular system. Whereas the role of brainstem function in the improvement of the contralateral ear's caloric response remains unclear it is also possible that hearing impulses affect the labyrinth. Clearly, the influence of cochlear implants on vestibular function requires further investigation to explain the improvement of contralateral vestibular responsiveness.