Cochlear implants: Who, how and why?
What is a cochlear implant?
A cochlear implant (CI) is a surgically small, complex implanted neuroprosthetic electronic device that replaces the function of the damaged inner ear. With the help of cochlear implants, the function of the damaged part of the inner ear is covered to provide sound signals to the brain.
Cochlear implant enables the sound to reach your brain bypassing the damaged ear part to directly starts stimulating the hearing nerve electronically.
Pros and Cons of cochlear implant
The pros and cons are considered as the important factor while weighing hearing amplification options for your child.
Hearing improvement: Cochlear implants can improve hearing abilities and make it better than ever before.
Speech Development: Cochlear implants improves and clears the child’s speech. As a result, it will make listening as well as speaking skills better in the future. Parents may use speech therapy techniques in order to enhance speaking skills of children with cochlear implants.
Future learning and career opportunities: Children with cochlear implants can hear better in the classroom, usually with the help of assistive technology. Cochlear implants open doors to new career opportunities. Thus this hearing experience will remove all the barriers of hearing in the school, colleges or institutions.
Safety: The candidate may hear potential dangers or alerts such as sirens and other important sounds with the help of cochlear implants. Thus besides providing incredible hearing experience, it also provides safety.
Confidence and independence: The cochlear implant boosts up the confidence of the candidate as they are able to experience better hearing. Thus they are independent of all the barriers of hearing and participate in social communication.
Surgery: The cochlear implants surgery involves certain risks, complication, and limitations associated with it.
Cost: The cost of a cochlear implant surgery will come under many insurance companies. If you do not have insurance, or if your plan does not cover the procedure, you will have to bear the complete cost of the surgery.
Background noise: Children will still need support hearing and communication in background noise. Assistive devices can help to hear in places with lots of background noise (classroom, car, zoo, etc). Thus the child may face problems due to these noises.
Maintenance: Cochlear implants require ongoing support, care, and maintenance. For example, you have to change the battery, fix the wire etc.
Outcomes and hearing levels differ for everyone: The advantages of the cochlear implant will differ from one person to another person. Various intervention programs will help to improve the outcomes of cochlear implants.
Childhood Activities: Children with a cochlear implant can enjoy their various recreative activities. However, they have to protect the device from damage, such as wearing a helmet while bicycling, or removing the device while swimming.
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
The 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
- Microphone is a small part that is placed behind the ear. The microphone picks the sound from the environment.
- The sound is received by the microphone and is sent to the sound processor.
- 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.
- 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.
- 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.
- 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.
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.
Cochlear implant accessories
Here is a list of the cochlear implant accessories to assist you in choosing the best devices for you.
- True Wireless Nuclear System
- True Wireless Baha System
- Kanso™ Sound Processor
- Nucleus 7 Sound Processor
- Nucleus 6 Sound Processor
- Nucleus 5 Sound Processor
- Other Nucleus accessories
- Freedom Hybrid System
- Baha® 5 Power Sound Processor
- Baha 5 SuperPower
- Baha 5 Sound Processor
- Baha 4 Sound Processor
- Baha 3 Power Sound Processor
- Baha 3 Sound Processor
- Baha Cordelle ll
- Baha Divino
- Baha Intenso
Who is a candidate for a cochlear implant?
The latest cochlear implant technology help those individuals who have –
- Individuals who have moderate to 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. 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.
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
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 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.
Profound 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.
Eligibility for children
- 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
The very first cochlear implant was approved by the FDA in the mid- 1980s for the treatment of hearing impairment in adults.
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.
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.
What is the process of cochlear implant?
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 the 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.
Cochlear implant 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 cochlear implant surgery is completed in the following steps :
- Surgeon gives you medication in order to sleep.
- Afterward, he makes a cut behind your ear and opens the mastoid bone.
- Along with the identification of the facial nerves, he creates the opening between facial nerves and mastoid bone to access the cochlea. Then he finally inserts the implant electrodes into the cochlea.
- The surgeon places the receiver under the skin behind the ear.
- Then at the final step, he closes all the incisions and you are moved into the recovery area.
What happens after surgery?
A patient may feel while walking:
- Pressure or discomfort over the implanted ear,
- Sick to the stomach,
- Disoriented or confused,
- 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.
Advantages of a cochlear implant
- You can 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.
The factors that affect the advantages
The outcomes of cochlear implants differ from one individual to other individuals. The reasons behind these differences are as follows :
- The duration of hearing loss before receiving a cochlear implant
- The severity of hearing loss
- The condition of the cochlea (inner ear)
- Other medical conditions like diseases, immunity, heredity etc
- The extent of practice they include in everyday life while using the cochlear implant.
Limitations 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, the cochlear implant may lead to distortion of noise. 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 the 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.