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Science 8 February 2002:
Vol. 295. no. 5557, pp. 1025 - 1029
DOI: 10.1126/science.1067796
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Viewpoint

Sending Sound to the Brain

J. P. Rauschecker,1 R. V. Shannon2

The cochlear implant, a microelectrode array that directly stimulates the auditory nerve, has greatly benefited many individuals with profound deafness. Deaf patients without an intact auditory nerve may be helped by the next generation of auditory prostheses: surface or penetrating auditory brainstem implants that bypass the auditory nerve and directly stimulate auditory processing centers in the brainstem.

Partial or total hearing loss has many different causes. Defects in either the outer ear or middle ear (composed of the tympanic membrane, ear drum, and auditory ossicles) result in a conductive hearing loss that can usually be remedied by insertion of a hearing aid, which amplifies sound vibrations. Profound deafness, on the other hand, is caused by loss of the sensory hair cells in the fluid-filled, snail-shaped inner ear, or cochlea, that transduce sound waves into electrical impulses, which are then transmitted to the brain (Fig. 1). Profoundly deaf individuals who still have an intact auditory nerve have profited from the dramatic advances made over the past 30 years in the field of cochlear implants (CIs) (1, 2). The CI is a microelectrode array implanted in the cochlea that directly stimulates the auditory nerve. With more than 40,000 patients worldwide, the success of these devices is nothing short of miraculous: Most adults are able to converse on the phone, and most children are able to be educated in mainstream classrooms. For some profoundly deaf individuals, however, even electrical stimulation of the inner ear with a CI is impossible owing to an absence or destruction of the auditory nerve. Instead, an auditory prosthesis consisting of a microelectrode array that directly stimulates one of the auditory processing centers of the brainstem, bypassing the cochlea and auditory nerve, might restore hearing to these patients. Such auditory brainstem implants (ABIs) have been under development since the late 1970s, pioneered by physicians and researchers at the House Ear Institute in Los Angeles (3), but have had only limited success. The next step in ABI evolution is already under way: Whereas conventional ABIs stimulate the surface of the ventral cochlear nucleus in the brainstem, the microelectrode array in the new generation of ABIs penetrates into the depths of the ventral cochlear nucleus, directly stimulating its neurons (nerve cells) (Fig. 2). This new approach has become feasible owing to the high-tech development of materials and electronics by researchers in the field of neural prosthetics (including CIs), as well as successful stereotactic studies carried out with permanent depth electrodes in cats, an animal with an auditory system similar to our own (4).

1 Department of Physiology and Biophysics, Georgetown University Medical Center, Washington, DC 20007, USA.
2 Department of Auditory Implants and Perception, House Ear Institute, Los Angeles, CA 90057, USA.

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Spatially Distinct Functional Output Regions within the Central Nucleus of the Inferior Colliculus: Implications for an Auditory Midbrain Implant.
H. H. Lim and D. J. Anderson (2007)
J. Neurosci. 27, 8733-8743
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From the Cover: Evidence that cochlear-implanted deaf patients are better multisensory integrators.
J. Rouger, S. Lagleyre, B. Fraysse, S. Deneve, O. Deguine, and P. Barone (2007)
PNAS 104, 7295-7300
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Auditory Cortical Responses to Electrical Stimulation of the Inferior Colliculus: Implications for an Auditory Midbrain Implant.
H. H. Lim and D. J. Anderson (2006)
J Neurophysiol 96, 975-988
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Effects of Electrically Coupled Inhibitory Networks on Local Neuronal Responses to Intracortical Microstimulation.
S. Butovas, S. G. Hormuzdi, H. Monyer, and C. Schwarz (2006)
J Neurophysiol 96, 1227-1236
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Bilateral Cochlear Implants in Adults and Children.
R. Y. Litovsky, A. Parkinson, J. Arcaroli, R. Peters, J. Lake, P. Johnstone, and G. Yu (2004)
Arch Otolaryngol Head Neck Surg 130, 648-655
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Localized Neurotransmitter Release for Use in a Prototype Retinal Interface.
M. C. Peterman, D. M. Bloom, C. Lee, S. F. Bent, M. F. Marmor, M. S. Blumenkranz, and H. A. Fishman (2003)
Invest. Ophthalmol. Vis. Sci. 44, 3144-3149
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Will Retinal Implants Restore Vision?.
E. Zrenner (2002)
Science 295, 1022-1025
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