Auditory Neural Prostheses – A Window to the Future.
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Date
2014-01
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Abstract
Hearing loss is one of the commonest congenital anomalies to affect children world-over.
The incidence of congenital hearing loss is more pronounced in developing countries like
the Indian sub-continent, especially with the problems of consanguinity. Hearing loss is a
double tragedy, as it leads to not only deafness but also language deprivation. However,
hearing loss is the only truly remediable handicap, due to remarkable advances in
biomedical engineering and surgical techniques. Auditory neural prostheses help to
augment or restore hearing by integration of an external circuitry with the peripheral
hearing apparatus and the central circuitry of the brain. A cochlear implant (CI) is a
surgically implantable device that helps restore hearing in patients with severe-profound
hearing loss, unresponsive to amplification by conventional hearing aids. CIs are
electronic devices designed to detect mechanical sound energy and convert it into
electrical signals that can be delivered to the cochlear nerve, bypassing the damaged hair
cells of the cochlea. The only true prerequisite is an intact auditory nerve. The emphasis is
on implantation as early as possible to maximize speech understanding and perception.
Bilateral CI has significant benefits which include improved speech perception in noisy
environments and improved sound localization. Presently, the indications for CI have
widened and these expanded indications for implantation are related to age, additional
handicaps, residual hearing, and special etiologies of deafness. Combined electric and
acoustic stimulation (EAS / hybrid device) is designed for individuals with binaural lowfrequency
hearing and severe-to-profound high-frequency hearing loss. Auditory
brainstem implantation (ABI) is a safe and effective means of hearing rehabilitation in
patients with retrocochlear disorders, such as neurofibromatosis type 2 (NF2) or
congenital cochlear nerve aplasia, wherein the cochlear nerve is damaged or absent on
both sides and hence, a cochlear implant (CI) would be ineffective. In such patients, the
brainstem implant bypasses the damaged / absent cochlear nerves and directly stimulates
the cochlear nucleus in the brainstem. The auditory midbrain implant (AMI) has been
designed for stimulation of the auditory midbrain, particularly the central nucleus of
inferior colliculus (ICC). It is used especially in patients with large neurofibromatosis
type 2 (NF2) wherein tumor induced damage to the brainstem/cochlear nucleus often coexists.
The efficacy and safety of auditory neural prostheses is well proven.
Advancements in technology will enhance the benefit provided by these prostheses.
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Kameshwaran Mohan. Auditory Neural Prostheses – A Window to the Future. Annals of the National Academy of Medical Sciences (India). 2014 Jan-June; 50(1&2): 57-74.