Auditory midbrain implant: Research and development towards a second clinical trial

Abstract

The cochlear implant is considered one of the most successful neural prostheses to date, which was made possible by visionaries who continued to develop the cochlear implant through multiple technological and clinical challenges. However, patients without a functional auditory nerve or implantable cochlea cannot benefit from a cochlear implant. The focus of the paper is to review the development and translation of a new type of central auditory prosthesis for this group of patients, which is known as the auditory midbrain implant (AMI) and is designed for electrical stimulation within the inferior colliculus. The rationale and results for the first AMI clinical study using a multi-site single-shank array will be presented initially. Although the AMI has achieved encouraging results in terms of safety and improvements in lip-reading capabilities and environmental awareness, it has not yet provided sufficient speech perception. Animal and human data will then be presented to show that a two-shank AMI array can potentially improve hearing performance by targeting specific neurons of the inferior colliculus. Modifications to the AMI array design, stimulation strategy, and surgical approach have been made that are expected to improve hearing performance in the patients implanted with a two-shank array in an upcoming clinical trial funded by the National Institutes of Health. Positive outcomes from this clinical trial will motivate new efforts and developments toward improving central auditory prostheses for those who cannot sufficiently benefit from cochlear implants.

Midbrain Synchrony to Envelope Structure Supports Behavioral Sensitivity to Single-Formant Vowel-Like Sounds in Noise

“…These findings indicate an incomplete transition to average-rate coding of vowellike sounds in the IC and underscore the significance of temporal discharge patterns for perception of complex sounds. Furthermore, they highlight the potential benefits of incorporating F0-related envelope structure into stimulation strategies for auditory midbrain implants, which currently provide inadequate temporal information for robust speech perception (Lim and Lenarz 2015). Finally, model simulations showed that average-rate coding of vowel-like sounds in quiet emerges from a synchrony-based representation in more peripheral nuclei due to amplitude-modulation tuning.…”

Auditory and audio–visual processing in patients with cochlear, auditory brainstem, and auditory midbrain implants: An EEG study

“…This underlines the importance of further AMI development including electrode design, stimulation strategy, and surgical procedure. In the second clinical trial, efforts are now under way to improve hearing performance in patients implanted with an AMI by reducing the effective stimulation rate per channel and by increasing the number of available stimulation channels with a double‐shank electrode [Lim and Lenarz, ]. With further extensive development, the AMI may turn out to be a device with a great future potential, especially for patients that cannot benefit from a CI or ABI.…”

“…The variability and limitation in outcomes with central auditory implants may have different causes: Neural damage might emerge due to the surgery, the electrode array may be placed inaccurately [Colletti et al, ], or the growth of bilateral cochleovestibular schwannomas in patients with neurofibromatosis type 2 (NF2) may cause damage in the cochlear nucleus [Behr et al, ]. Moreover, central auditory implants do not yet have suitable electrode array designs and the used CI processing strategies are not optimized for stimulation of more centrally located nervous structures [Lim and Lenarz, ; McKay et al, ].…”

Recognizing the journey and celebrating the achievement of cochlear implants

“…Ling et al (2015) review the conception and research of vestibular implants to treat balance-related disorders including disequilibrium, oscillopsia, or vertigo. Lim and Lenarz (2015) describe the development and translation of the auditory midbrain implant for patients without a functional auditory nerve or implantable cochlea. To overcome the intrinsic limitations related to broad electric stimulation, novel optogenetic stimulation has been proposed to demonstrate the proof of principle in developing an optical cochlear implant (Jeschke and Moser, 2015) and an optical auditory brainstem implant (Hight et al, 2015).…”