Cochlear Implant Associate With Development Of Speech Perception

What is the Cochlear Implant?

A cochlear implant (CI) is a surgically small, complex implanted neuroprosthetic electronic device that replaces the function of the damaged inner ear. Cochlear implants offer a sense of sound to people with severe to profound sensorineural hearing loss (70 to 90 dB) who do not benefit from hearing aid. Cochlear implant enables the sound to reach your brain bypassing the damaged ear part to directly starts stimulating the hearing nerve electronically.

Cochlear implant

History

Around two centuries ago(1800), Alessandro Volta inserted a metal rod in his own ears and stimulating them to electric current. He also confirmed that he created a hearing sensation. In 70’s  Dr. William House, invented the first single-channel cochlear implant.

After single-channel, Graeme Clark from Australia, and Ingeborg Hochmair and also with her future husband, Erwin Hochmair, developed and also commercialized a modern multichannel cochlear implant.

How does cochlear implant work?

Cochlear implant (CI) usually pass the peripheral auditory system which normally collects the sound and then converts that received sound into hair cells movement in the cochlea. These hair cells inside part release potassium ions in reaction to the hair cells’ movement. Therefore, the potassium also stimulates other cells in order to release neurotransmitter, glutamate. All this makes the cochlear nerve to send a signal to the brain which in turns produces a sound experience.

Here the cochlear implant parts collect the sound and digitize the sound. Then, converts the digitized sound into electrical signals and transmit the digitized signals to the electrodes implanted in the cochlea. The electrodes start stimulating the cochlear nerve, sending the signals to the brain.

Parts of cochlear implant

Cochlear implantThe cochlear implant has two main parts –

  • External component:- The external (outside) part which sits behind the ear and it contains a microphone, a speech processor, and a transmitter.
  • Internal component:-  An internal (surgically implanted) parts that work together to allow the user to perceive sound. It consists of receiver/stimulator and an electrode array.

Step by Step working of cochlear implant

Step 1 – Microphone is a small part that is placed behind the ear. The microphone picks the sound from the environment.

Microphone of the cochlear implant
The microphone of the cochlear implant

Step 2 – The sound is received by the microphone and is sent to the sound processor.

Sound from Microphone to speech processor

Step 3 – The Reciever or stimulator then start analyzing and digitizes the received sound into a coded signal. Then, the coded signal is sent to the transmitting coil.

Step 4 – The transmitting coil then sends the coded signal to the skin of the stimulator or the receiver of the internal component of the cochlear implant.

Reciever or stimulator

Step 5 – Then the signals are sent to the electrodes to start stimulating the remaining nerve fibers. These electrodes directly stimulate the auditory nerve throughout a portion of the cochlea.

Electrode of the cochlear implant

Step 6 – The signals are recognized by your brain as sounds and therefore produces a hearing sensation.

How many channels are in a cochlear implant?

Channels can be thought of as the output of filter banks. Theoretically, each channel in a cochlear implant can be made to correspond to a single electrode (1-to-1 mapping). However, this has not been applied in practice because closely spaced electrodes may not produce truly different sound percepts.

In other words, two or more electrodes may stimulate the same auditory nerve ending and produce only one pitch percept. Thus, too many electrodes may lead to redundancy between electrodes, and decrease their ability to deliver distinct sound frequencies. However, having more electrodes available may offer a different kind of benefit. Sometimes, regions of the cochlea may not be responsive to electrical stimulation.

If we had more electrodes, one could stimulate adjacent responsive regions using a different subset of electrodes. Hence, having more electrodes would be theoretically beneficial in programming CIs in the presence of problem locations within the cochlea. Cochlear implants help hearing loss people.

Stimulation Modes

Another reason there is no “1-to-1” mapping between channels and electrodes is that the number of available electrodes for stimulation depends on the mode of stimulation used. There are 2 fundamental modes of stimulation employed by the Cochlear implants (CI) to deliver the electrical current to the auditory nerves. The first is monopolar and the second is bipolar.

Single Channel and Multichannel

CI manufacturers have developed 2 basic types of CIs; single channel and multichannel devices. To transfer acoustic information to the brain via electrical signals, all CI systems need to closely adhere to the ”natural” laws of signal transfer, as demonstrated and employed by the normally functioning cochlea. That is, researchers must consider how best to code speech signals electrically, in a way that will make the best use of the cochlea’s anatomic organization and mimic the natural processes occurring within the auditory system.

The information contained in the speech signal can be grossly divided into intensity and frequency subcomponents. Each of these can be electrically transferred via the CI to the brain. For example, a bipolar (BP) +1 mode (active and reference electrodes separated by one non-active electrode) of stimulation will sound louder than a BP mode, given the same level of current applied, because more nerve fibers will be stimulated in the former case. Frequency coding depends on the rate of nerve firing (temporal theory) and the place of stimulation along the length of the cochlea (tonotopic or place theory).

Single channel CIs code frequency based on the rate of firing of electrical pulses. Multichannel CIs use the place theory strategy for coding frequency, wherein different frequencies from the auditory signal are separated and presented in a tonotopic manner along the length of the cochlea via the electrode array. The place theory strategy of coding is currently utilized by most CI manufactures.

What are the Differences Between Cochlear Implants and Hearing Aids?

There is one cochlear implant implanted for every 16,000 hearing aids. According to the estimates of the U.S. Food and Drug Administration [FDA], in the US, around 38,000 cochlear devices implanted in children and 58,000 devices in adults in comparison to 12 million American who wear hearing devices. It is very important to note that for one person wearing CIs, they are around 125 individuals who wear hearing aids. Also, there is 0.5 percent of people, who are taking treatments for sensorineural hearing loss will use cochlear implants.

There are many factors that make the working and other function of a cochlear implant and hearing aid different. Few of the differences are listed below-

Hearing aids vs Cochlear implant

  • Hearing aids amplify the sound then deliver the amplified sound to the damaged cochlea. The programming of hearing aid depends on the type of hearing loss. On the other hand, a cochlear implant transforms the sound into an electrical signal. These electric signals work with the auditory nerve and the brain and then the sound is interpreted.
  • The cochlear implant is best for an individual with a severe to profound hearing impairment and the hearing devices are best for those users who got the hearing difficulty due to noise-induced hearing loss.
  •  The cochlear implant helps people in making regular conversation, understanding environmental sound while hearing aid users struggle with the volume of sound.
  • Hearing aids user will get benefit immediately but cochlear implant doesn’t give any guarantee.
  • The cochlear implant needs surgery but there is no surgery required for hearing devices.
  • The cost of a cochlear implant and the surgery is very high as compared to hearing machine.
  • The batteries of the cochlear implant didn’t last as hearing aid batteries.

Who is a candidate for a cochlear implant?

The latest cochlear implant technology help those individuals who have –

  • Individuals who have moderate to a profound hearing impairment in both ears,
  • People who got the score of 50 percent or less on sentence recognition tests taken by the specialist in the ear to be implanted,
  • For those who get a little or no benefit from the use of hearing devices,
  • Individuals who got the score of 60 percent or less on sentence recognition tests taken by the specialist in both ears with hearing machine or the non-implanted ear.

According to NIDCD, around December 2012, approx 324,200 cochlear devices have been implanted around the world.

Hearing impaired adults and Kids who have hearing difficulty can be fitted with a cochlear implant. According to the estimates of the U.S. Food and Drug Administration [FDA] In the US, around 38,000 cochlear devices implanted in children and 58,000 devices in adults.

The very first cochlear implant was approved by the FDA in the mid- 1980s for the treatment of hearing impairment in adults. From 2000, FDA approved cochlear implants for children up to 12 months of age. For kids who are hearing impaired or have hard-of-hearing difficulty, with implanted cochlear devices as there young ears get exposed to sounds during an optimal period for the development of speech and language skills.

Some scientific studies and research have pointed out that these kids receive a cochlear implant with an intensive therapy. Before the time these children became 18 months old, they should develop the hearing ability, also should understand music and different sounds. Many studies have pointed out that kids who got cochlear implants before attaining the age of 18 months have developed language skills at a comparable rate to kids with normal hearing. And also there are many who successfully succeed in classroom activities.

Adults who are deaf can also benefit from cochlear devices. Gradually they learn to link the signals from the device with the sound they try to remember such as speech instead of asking any type of visual clues such as those given in sign language and lipreading.

A cochlear implant can be used by both children and adult according to their hearing loss. The FDA (US food and drug administration) approves criteria when new devices are brought to market but insurance companies also set criteria of their own. As a result, cochlear implant candidacy is usually determined on a case-by-case basis.

Cochlear implant for children

Cochlear plant in a childProfound deafness in childhood affects the development of auditory speech perception, speech production, and skills. A child with hearing loss can affect the development of themselves. A cochlear implant can give these children renewed hope for the future by providing useful hearing with access to environmental sounds and spoken language. Children with hearing impairment as young as 1 year old can be eligible for a cochlear implant. Children are considered viable candidates when they:

  • Have profound hearing loss in both ears.
  • Get little or no benefit through the use of hearing aids.
  • Are healthy and any medical conditions would not compromise surgery.
  • Understand along with their parents, their role in the successful use of cochlear implants.
  • Have support from an educational program that will emphasize the development of auditory skills.

Cochlear implant for Adults

A cochlear implant provides access to sound for people with severe or profound hearing loss, who can no longer hear with hearing aids. Adults who face a hearing problem after their development typically have greater success with cochlear implants than those who had not developed language before losing their hearing. Adult candidates are generally eligible for an implant if they:

  • Have severe or profound hearing loss in both ears.
  • Get little or no benefit from hearing aids.
  • Have no medical problems that could put them at risk during surgery.
  • Have a strong desire to be part of the hearing world and communicate through listening, speaking, and speech reading.

Criticism and controversy

Criticism and controversy for cochlear implantThe major objection for cochlear implantation has come from within the Deaf community. The deaf community carries a perception that there is nothing to be fixed. Deaf community critics believe that the CIs are an affront to their community as they see it as a threat coming from hearing majority. A strong disagreement since the 18th century is being carried out when the difference between the abnormal and normal started to be debated.

Individuals of the deaf community believe that they have a unique culture and language. Therefore, they consider cochlear implantation as an affront to their unique culture because according to them deafness is not something to be cured. But its argued that the CIs can be used as a tool for the deaf people to mark their existence in the “hearing world” with any kind of lose their Deaf identity.

It is considered that the deaf children are found to be very effective with implanted with CIs at a young age. As at this critical young age kids brain are still learning to interpret sound. But Deaf culture believes that as the implants do not produce normal hearing so they will make a self-image of the deaf kids as a “disabled” instead of being a proud deaf person. Also, some of the extreme responses considered the cochlear implantation as a “cultural genocide”.

With the growing trend of CIs, some deaf community critics made an effort to oppose the “either-or” formula of oralism vs manualism also with a “both-and” approach. Today there are some educational institutes which successfully combined the sign language with CIs in their study programs.

What is the process for getting an implant?

Pre Surgery

An individual who requires a cochlear implant need an initial referral and for that he/she should consult an audiologist or an ENT physician for a referral to a cochlear implant center. At the center, the candidate will undergo a full medical evaluation which involves psychological and audiological testing, a medical exam and also imaging studies to access level and type of hearing. Also to make sure that if they will get proper advantage from a cochlear implant. There will also be auditory training and post-training evaluation for all the individuals. After the training,  counseling is also compulsory for the candidate, to make sure he/she and also child and their parents, understand the large follow-up commitment needed after the cochlear implant surgery, as well as the requirements regarding the device performance and limitations.

Surgery

Cochlear implant surgery lasts about two to three hours and is performed while the patient is under general anesthesia. It is done by an implant team otology surgeon, a cochlear implant audiologist, a radiologist, and, as needed, a social worker, a psychologist or psychiatrist, and/or an education specialist, who will give you a series of tests.

The surgeon place the cochlear implant behind the ear. Then, the implanted receiver is attached and the electrode array is carefully inserted into the cochlea. Before completing surgery, the implant is checked to ensure that it is working properly.

What happens after surgery:

 a patient may feel while walking:

  • pressure or discomfort over the implanted ear,
  • dizziness,
  • sick to the stomach,
  • disoriented or confusion,
  • a sore throat for a while from the breathing tube used during general anesthesia.

Then, a patient can expect to:

  • keep the bandages on for a while,
  • have the bandages be stained with some blood or fluid,
  • go home in about a day after surgery,
  • have stitches for a while,
  • get instructions about caring for the stitches, washing the head, showering, and general care and diet,
  • have an appointment in about a week to the stitches removed and have the implant site examined,
  • have the implant “turned on” (activated) about 3-6 weeks later.

 Risks and Complications

There is always some risks and complications with cochlear implant surgery. We have discussed some below:

General Anesthesia risks-

General anesthesia is a drug-induced sleep. The drugs like anesthetic gases or injected drugs can affect people differently. Mostly, it is not riskier but for some people with some medical problems, it may be risky. The standard surgical risks of a cochlear implant are all quite extinct.

It includes bleeding, infection, device malfunction, facial nerve become weak, tinnitus (ringing in the ear), dizziness, and bad hearing result. One long-term risk of a cochlear implant is meningitis (infection of the fluid around the brain).

Risks of the procedures include mastoiditis (Mastoiditis is an infection of the spaces within the mastoid bone), otitis media (an infection in the middle ear acute or with effusion). Shifting of the implanted device requires a second procedure, damage to the facial nerve, chord tympani, and wound infections.

People may experience problems with dizziness (a reeling sensation, a feeling that you are about to fall)  and balance for up to a few months after the procedure. These issues typically resolve except for individuals at age seventy.

Facial nerve stimulation usually occurs in patients with anomalous ear or even in those without any specific pathology. Poor response of the auditory nerve is rare, but it may occur in children who are born deaf or in adults who are post-lingually deaf and infections occur in only a limited number of cases.

Cochlear implant Cost

A Cochlear implant cost depends on the variety of factors, including the duration and extent of a patient’s hearing loss prior to surgery. The average cost for the entire procedure, including the post-operative aural rehabilitation process, exceeds $40,000.

However, cochlear implantation consistently ranks among the most cost-effective medical procedures ever reported, according to research completed by the Johns Hopkins University and the University of California-San Diego. These studies indicate that cochlear implantation can result in a net savings of more than $53,000 per child versus the more than $1 million average expected lifetime cost of a child who has profound hearing loss prior to language development. Following are the cost comparison in a different country:

CountryIndiaUSTurkeyUAE
Cochlear implant surgery cost ($)$ 6000$80000$ 21,906$9600

Do insurance companies pay for cochlear implants?

As cochlear implantation is considered to ba standard treatment for sensorineural hearing loss, therefore CIs are covered by Medicaid or Medicare and other private and commercial insurers. In 2004, more than 90 percent of all medical insurers including the Veteran’s Administration, Medicaid, and Medicare covers the CIs. Also, Cochlear implant centers consider obtaining prior authorization from the insurance companies before going for cochlear implant surgery.

Medicare

Under the statutory Medicare benefit, cochlear implants are covered for prosthetic devices. As per the National Coverage Determination, Medicare provides the insurance coverage for patients having sensorineural, moderate-to-profound hearing impairment in case they need cochlear implantation. The insurance benefit is also limited and depends on the test scores of equal to or less than 40 percent for sentence understanding in the best-aided listening conditions.

Medicare covers the cochlear implants for all the patients who fulfill all the coverage criteria without regard to whether the CIS is bilateral or unilateral. Also, the rules for medical reimbursement are extremely complex but still they can alter depending on the condition.

Research on the age limit for the Cochlear implantation

By the age of three, children with hearing impairment need to hear approximately 25,000-30,000 words a day to develop the language skills and it is also very necessary to succeed in school and everyday life. So, if a child is born deaf or with any sort of hearing loss. Then, they are missing out on the important inputs of sound. However, cochlear implantation at an early age helps to adjust to the situation. That’s why babies use cochlear implant and hearing aids at a very young age.

According to NCBI, both the adults and children get to benefit from cochlear implantation. Also, at the end of the research, there is no significant age-related difference found in an individual with a unilateral implant, nor in CI with an acoustic hearing aid in the non-implanted ear. In the bilateral cochlear implant, younger children had shown a gradual increase in both self-rated abilities and performance whereas as the adults had shown mixed outcomes.

Cochlear Implant Frequently Asked Questions

What does a cochlear implant sound like?

A cochlear implant doesn’t actually produce noise. The channels that implant users specifically designed in order to amplify speech and make it more interpretable. But they are not doing a good job at replicating the real world sounds. The implants especially are not useful at replaying the pitch, therefore, it becomes hard to understand the tonal languages such as Chinese or to differentiate individual noises in a crowd.

Researchers making their effort to make cochlear implants clearer but the best implants we have, make the world sound very different but for those who choose to use cochlear implants, it is a way to listen to a speech, even it sounds strange. The common sound qualities in the cochlear implant are described as robotic, mechanical or cartoonish, it is sounds as if someone is taking with marbles in their mouth.

Most of the patients start feeling the stimulation when the implant is first turned on. It is very important to keep in their mind that is a process. With time quality of sound will change as gradually the brain starts learning the stimulation patterns given by the cochlear implant. In maximum cases, the sound quality will eventually improve with time.

Can I go swimming or take a shower after getting a cochlear implant?

Yes, one can shower wear a cochlear implant. The implant is surgically placed underneath the skin of the patient, which makes it waterproof. Although the external processor traditionally is not waterproof, so it needs to be removed before going into water such as scuba diving. Some of the latest models available of external processors have waterproof options so, you can wear them inside water or while taking a shower. For further knowledge, you can discuss your options with an audiologist or check with the manufacturer to what depth you can dive with the internal implant.

How frequently do I need to come for appointments after I get a cochlear implant?

For every one of us, having a cochlear implant is like a lifelong commitment. After the surgery, you need to visit the specialist around three to four times. These visits with the specialist will help you in giving the important transitional period which helps you in adapting to the new sounds you will start hearing with the help of your CI. For the first two years, you need to make your visits every three to six months and then every next year after that.

Can I wear a cochlear implant while sleeping?

No, you should not wear the implant while sleeping as it can get damaged. Specialist suggests that you should remove your devices before going to bed. In case you live alone, then you can also consider buying additional assistive listening devices so that you can get an alert for removing your devices.

How much hair will be shaved off during surgery?

The surgeon will only shave a very little area of hair at a place behind the ear of around 1 cm to 2 cm.

Can you play active sports if you have cochlear implants?

Yes, you can play active sports while wearing a cochlear implant. Although, it is important to wear headgear so that you can protect your audio processors.

What is the importance of speech therapy after cochlear implantation?

Speech therapy or rehabilitation play a major role in the outcomes. Cochlear implant therapist or an Auditory Verbal Therapist provide the patient with training which helps him/her in hearing through the cochlear implant. And as per the norms also helps speech & language development. The outcomes may vary from patient to patient depending on the age of the patient at which he/she get the implant. In these programs for better outcome parents also try to involve themselves at maximum extent.

Outlook

Advantages of a cochlear implant

  • Hear better with a cochlear implant compare to hearing aids.
  • With cochlear implant achieve an average of 80% sentence understanding, compared with 10% sentence understanding for hearing aids.
  • Easy focus on the noisy environment.
  • Can easily interact with people across meeting tables, in restaurants and other crowded places.
  • Reconnect with missed sounds that they could not hear before their cochlear implant.
  • Feel safer in the world as they can hear alarms, people calling out and approaching vehicles.
  • Talk and hear on the phone.
  • Enjoy the music.

Disadvantages of cochlear implants:

  • Some time a cochlear implant does not fulfill their goal or does not improve hearing loss.
  • The cost of implantation is very high and many people not able to afford the cost of the implant.
  • In some cases after cochlear implant Noises are distorted. The adult takes more time than children to re-adjusting sounds.
  • It may cause permanent damage to an auditory nerve.
  • The cochlear implant may increase a chance to develop bacterial meningitis.
  • It can cause muscle spasms, numbness, facial paralysis.
  • People can’t enjoy high-contact sports and water activities. That may damage cochlear implants.
  • It requires regular maintenance such as replacing batteries, replacing wires, fixing processor. It is a very expensive process and some time also needs to replace the implant.
  • Some time people face irritation and infection around the implant.
  • Some internal problem occurred in a cochlear implant after implantation.
  • The static electricity can damage electrical component of the implanted device and may erase program that process sound or speech.
  • The child started playing with their cochlear implant and it may damage due to their childhood activities.

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Cochlear Implant Associate With Development Of Speech Perception
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