Cochlear implant

Refers to the implant of an electrode array into the cochlea and uses a microphone near the ear to receive acoustic signals and then transmits the stimuli to the electrode, which then stimulates the cochlear nerve.

A cochlear implant is an electronic device that replaces the cochlea of the inner ear. 

Electrodes are typically inserted through the round window of the cochlea, into the fluid-filled scala tympani. 

They stimulate the peripheral axons of the primary auditory neurons, which then send information to the brain via the auditory nerve. The cochlea is tonotopically mapped in a spiral fashion, with lower frequencies localizing at the apex of the cochlea, and high frequencies at the base of the cochlea, near the oval and round windows. 

Cochlear implants acquire and process the sound and convert it into electrical energy for subsequent delivery to the auditory nerve. 

Compared with hearing aids that amplify acoustic information, cochlear implants bypass the normal transduction mechanism of the peripheral auditory system and directly stimulate the auditory nerve using an electric signal.

For patient with poor speech recognition and more advanced bilateral sensorineural hearing loss, cochlear implantation provides the only effective means of auditory rehabilitation.
While hearing aids function by amplifying sound, cochlear implant bypass nonfunctional or a missing cochlear hair cells and directly stimulates surviving spiral ganglion cells of the distal cochlear nerve, enhancing both auditory and speech recognition.

The processor digitizes the sound and filters it into separate frequency bands that are sent to the appropriate tonotonic region in the cochlea that approximately corresponds to those frequencies.

Sound intensity is controlled by modifying current amplitude impulse duration individual electrode contacts.

 It is a relatively low risk outpatient procedure that generate leads to improvements in speech understanding and quality of life.
During unilateral cochlear implant surgery the typical time under anesthesia is less than two hours and is associated with limited blood loss.

 Perioperative anesthetic risks are relatively low.

These devices substitute the functions performed by the eardrum and stapes while simulating the frequency analysis performed in the cochlea.

Devices share similar designs: an external component contains a microphone, battery, sound processor, and transmitting coil, and the internal component includes a radio frequency receiver coil, microprocessor-based stimulator, and multi channel electrode.
The internal component is surgically placed, and consists of an electrode array that is advanced into the cochlea and a receiver stimulator.
The entry cochlear electrode contains 12-22 active contacts that independently stimulate different regions of the cochlea.
Virtually all current sound processors integrate smart phone and wireless Bluetooth technology.
They are safe for MRI imaging.

Less than 10% of adults in the US who meet the criteria for cochlear implantation receive this treatment.

A microphone on an external unit gathers the sound and processes it; the processed signal is then transferred to an implanted unit that stimulates the auditory nerve through a microelectrode array.

Due to spatial constraints, the cochlear implant may not be inserted all the way into the cochlear apex. 

It provides a different kind of sound spectrum than natural hearing, but may enable the recipient to recognize speech and environmental sounds.

Neurosensory cells collect low frequency aggregate in the apex of the cochlea and those that collect high frequencies aggregate in the base.
This arrangement allows a cochlear implant’s electrode to selectively activate different regions of the cochlea to control pitch.
This tonotopic organization of the cochlea allows shortened length electrodes, used in hybrid cochlear implant‘s to treat mid and high frequency hearing loss through preferential electrical stimulation of the basal cochlear while simultaneously preserving preoperative low frequency acoustic hearing by limiting trauma to the more ethical regions of the cochlea.

Through the replacement or augmentation of damaged senses, these devices intend to improve the quality of life for those with disabilities.

Effective in children, adults with profound hearing loss.

More than half of young children with severe senorineural hearing loss are treated with cochlear implants.

Cochlear implants have allowed acquiring of spoken language development in congenitally deaf children, with remarkable success in implantations before 2–4 years of life have been reached.


There  have been about 80,000 children implanted with cochlear implants worldwide.

The system transforms acoustic cues into an electrical code.

Individuals can understand speech, environmental sounds and music with varying degrees of success.

Earlier intervention with cochlear implants results in more successful language performance.

Childhood Development after Cochlear Implantation studied spoken language in children who underwent implantation prior to age 5 years: the use of cochlear implantation was associated with better spoken language learning than would have been predicted from preimplantation scores (Niparko JN).

Cochlear implantation is associated with improved comprehension, and expression of spoken language over the first 3 years of implant use.

Cochlear implant is typically activated 2-4 weeks after implantation.
Cochlear implant surgery is a relatively low risk outpatient procedure performed while the patient is under general anesthesia.
The complication rate of cochlear implant surgery is about 12.8% and include wound infections, hematoma, chronic surgical site pain, persistent vestibular symptoms, and permanent facial nerve paralysis.
The risk of postoperative meningitis is associated with an age of less than six years with the presence of inner ear malformations, and it’s prevalence is less than 0.1%.
Device failure requiring reimplantation occurs in about 1.9% of cases.
Approximately half of adults who have functioning preoperative acoustic hearing, lose this residual hearing as a complication of surgery.
After implementation there is a period of acquisition where voice sound pitch and sound quality are monitored and adjusted.
Speech perception improves after cochlear implant implantation, usually within the first six months of use, but improvement can occur for up to three years.
Up to 16% of adults cochlear-implant recipients of poor long-term outcomes.

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