Definition: A cochlear implant is an electronic device that can provide useful hearing and improved communication abilities for persons who have severe to profound sensorineural hearing loss and who cannot benefit from hearing aids.
Components of Cochlear Implants
A cochlear implant has an external and internal component:
1. External component: It consists of an external speech processor and a transmitter.
2. Internal component: It is surgically implanted and comprises the receiver/stimulator package with an electrode array.
How it works?
Sound is picked up by the microphone in the speech processor. The speech processor analyses and codes sounds into electrical pulses.
The electrical impulses are sent from the processor to the transmitting coil which in turn sends the signal to the surgically implanted receiver/stimulator via radiofrequency.
The receiver/stimulator decodes the signal and transmits it to the electrode array inside the cochlea to stimulate the spiral ganglion cells. The auditory nerve is thus stimulated and sends these electrical pulses to the brain which are finally interpreted as sound.
Prerequisites of cochlear implantation:
1. Bilateral severe to profound SNHL.
2. Little or no benefit from hearing aids.
3. No medical contraindication for surgery.
4. Realistic expectation.
5. Good family and social support toward habilitation.
6. Adequate cognitive function to be able to use the device.
Candidates with such hearing impairment may be defined as prelingual or postlingual depending on whether they were deafened before or after the acquisition of speech.
In children who have hearing impairment at birth or early in childhood, early intervention with hearing aids or a cochlear implant is vital for auditory stimulus. Auditory deprivation, i.e. lack of auditory stimulus in the early developmental period causes degeneration in the central auditory pathways. This will limit the benefit in terms of speech and language acquisition following cochlear implantation.
Factors that predict a successful clinical outcome are:
1. Previous auditory experience (postlingual patients or prior use of hearing aids).
2. Younger age at implantation (especially for prelingual children).
3. Shorter duration of deafness.
4. Neural plasticity within the auditory system.
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