The auditory midbrain implant (AMI) is a new hearing prosthesis designed for stimulation of the inferior colliculus in patients who do not receive sufficient benefit from cochlear or brainstem prostheses. We have begun clinical trials in which three patients have been implanted with the AMI. Although the intended target was the central nucleus of the inferior colliculus (ICC), the electrode array was implanted into different locations across patients (i.e., ICC, dorsal cortex of inferior colliculus, lateral lemniscus). In this paper, we will summarize the effects of electrical stimulation of these different midbrain regions on various psychophysical properties and speech perception performance. The patient implanted within the intended target, the ICC, exhibited the greatest improvements in hearing performance. However, this patient has not yet achieved open-set speech perception to the performance level typically observed for cochlear implant patients, which we believe is partially due to the location of the array within the ICC. We will present findings from previous AMI studies in guinea pigs demonstrating the existence of spatially distinct functional output regions within the ICC and suggesting that further improvements in performance may be achieved by stimulating within a rostral-ventral region. Remaining questions include if a similar organization exists in the human ICC and if stimulation of its rostral-ventral region with currently available strategies (i.e., those designed for cochlear implants) can restore sufficient speech perception.
Bibliographical noteFunding Information:
Human studies : We would like to thank Rolf-Dieter Battmer, Gert Joseph, Urte Rost, and Joerg Pesch for involvement with AMI patient testing and fitting; Madjid Samii, Amir Samii, and the International Neuroscience Institute (Hannover, Germany) for AMI surgery; and James F. Patrick, Frank Risi, and Cochlear Ltd. (Lane Cove, Australia) for AMI development and technical assistance. We also thank Hans-Joachim Kretschmann, Martin Bokemeyer, and the Anatomy and Neuroradiology Departments at Hannover Medical University for CT-MRI reconstructions and identification of the AMI array location in each patient. Funding was provided by Cochlear Ltd. Animal studies : We would like to thank James Wiler, Guenter Reuter, Alexandru C. Stan, Uta Reich, Gerrit Paasche, Nadine Marquardt, Marc N. Klingberg, and Anke Neuheiser for involvement with the electrophysiology and chronic studies; and Jamille Hetke and the University of Michigan Center for Neural Communication Technology (NIH P41 EB2030) for multi-site stimulation and recording probes. Funding was provided by NIH through P41 EB2030, P30 DC05188, T32 DC00011, and F31 DC007009; Cochlear Ltd.; German Research Foundation (SFB 599); and the University of Michigan Center for Wireless Integrated MicroSystems (NSF Engineering Research Center).
- Auditory brainstem implant
- Auditory midbrain implant
- Central auditory pathways
- Deep brain stimulation
- Functional zones
- Inferior colliculus