Auditory Midbrain Implant: A Review

Abstract

The auditory midbrain implant (AMI) is a new hearing prosthesis designed for stimulation of the inferior colliculus in deaf patients who cannot sufficiently benefit from cochlear implants. The authors have begun clinical trials in which five patients have been implanted with a single shank AMI array (20 electrodes). The goal of this review is to summarize the development and research that has led to the translation of the AMI from a concept into the first patients. This study presents the rationale and design concept for the AMI as well a summary of the animal safety and feasibility studies that were required for clinical approval. The authors also present the initial surgical, psychophysical, and speech results from the first three implanted patients. Overall, the results have been encouraging in terms of the safety and functionality of the implant. All patients obtain improvements in hearing capabilities on a daily basis. However, performance varies dramatically across patients depending on the implant location within the midbrain with the best performer still not able to achieve open set speech perception without lip-reading cues. Stimulation of the auditory midbrain provides a wide range of level, spectral, and temporal cues, all of which are important for speech understanding, but they do not appear to sufficiently fuse together to enable open set speech perception with the currently used stimulation strategies. Finally, several issues and hypotheses for why current patients obtain limited speech perception along with several feasible solutions for improving AMI implementation are presented.

Directing neuronal cell growth on implant material surfaces by microstructuring

“…[12][13][14] In previous experiments, a reduced fibroblast growth on microstructured platinum surfaces was demonstrated. 15 Further optimization of the electrode-neuron interface could be achieved by directing the orientation of neurons, especially in central auditory prosthesis with close contact to the neurons, such as AMI 16,17 and ABI. 18 Parallel microgrooves on surfaces of various materials had been shown to promote the alignment of neuronal cells, [19][20][21][22][23][24][25] astrocytes, 26,27 as well as fibroblasts.…”

Interfacing with the nervous system: a review of current bioelectric technologies

“…Although historically NF2 patients have had exceedingly limited benefit from ABIs due to the detrimental nature of the tumors, more recent studies from Europe have reported considerable success in ABI performance in NF2 patients, including a mean open-set speech perception of 41% at 24 months post-ABI activation in 18 NF2 patients [77]. Notably, a penetrating ABI and an auditory midbrain implant inserted into the inferior colliculus did not lead to an increased benefit over the ABI [69,70,138].…”

The Evolution of Neuroprosthetic Interfaces

“…Worldwide, more than 100,000 people with hearing loss use cochlear implants to compensate for their impairments, and they can even hear and understand speech. 135 Similarly, retinal stimulation can elicit visual percepts in patients with vision loss. 136,137 Ongoing development of electrodes and stimulation parameters has provided basic letter recognition, orientation, and improved visual acuity in blind patients.…”