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Cochlear Implants

August 24, 2010

This is a guest post by Arron Brown. Thanks to Arron.

Definition of a Cochlear Implant

A Cochlear implant is a small surgically implanted device which helps improve the hearing abilities of profound or entirely deaf people. The device does not restore or replicate normal hearing, but it gives the user a sense of sound which is enough to help them understand speech.

There are over 200,000 cochlear implants in use worldwide, generally found in the West due to the costs associated with the materials and technology, the implant surgery and the post-implantation therapy needed. In recent years, bilateral implants are becoming more commonplace (one implant in each ear).

The device comprises of a;
•    Microphone that can pick up sounds from the environment,
•     Voice processor which selects sounds picked up by the microphone
•    Transmitter and stimulator which receives sound signals from the voice processor and convert them into electric impulses,
•    And an electrode array which is a group of electrodes that collects the impulses from the stimulator and sends them to the cochlea to be carried to the brain via the scala tympani.

The actual implant is placed beneath the skin behind the ear, and the transmitter and the electrode array is placed in position so that external movement will not misplace them. Externally, the microphone covers this location, connected to the voice processor, which usually fixes behind the ear like any other hearing aid. Some voice processors are too large for this location, so can be worn in a pouch, on the belt, or on a collar. The larger the voice processor, the greater the ability of a system to pick out and amplify the relevant speech sounds. Because electronic technology is improving at a rapid pace, it is expected that these larger voice processors will soon become outdated.  There are also far advanced models that can be fully implanted, but not without problems (battery replacement, microphone location), however they are not suitable for wide scale use yet.

The current method for transmitting the data is through radio frequency. The microphone is held in place over the implant via a magnet in the implant. There is no physical connection of the two parts whilst the device is working to limit the change of infection. This also means that the device can be removed for sleeping, battery replacement and upgrades.

With regards to education, there are currently many Schools in the UK that cater for hearing impaired pupils, one of which is St Johns’ Catholic School based in Leeds. The School caters for ages 3 – 19 and has three main educational departments, one of which is the Primary Department which caters for the needs of deaf children aged from 3 to 11 years of age.

How do Cochlear Implants Work?

A Cochlear Implant differs from the previous technologies available, such as conventional hearing aids. Cochlear Implants directly stimulate the Cochlea and the auditory nerve whereas hearing aids only amplify sounds so that they can be detected by damaged ears.

Sounds in the air lead to resonant vibrations on the basilar membrane in the Cochlea. High pitch sounds create vibrations that do not pass very far over the membrane, whereas low pitch sounds create vibrations that stretch further. These vibrations cause disturbance to microscopic hair around the membrane, which can be picked up by surrounding nerves. The brain is able to interpret which area of the membrane is vibrating, so can therefore represent the correct sound that is being made.

Hearing aids, by increasing the sound volume can give the user an idea of the sounds that are around them so that damaged hairs can still be stimulated if the volume is high enough. Cochlear Implants send a different type of signal to the brain via the same nerve systems. This means those who get an implant will have to learn or relearn how to process this information. Once learnt, sounds can be recognised quite well, to an extent, and users can enjoy a relatively normal life of hearing.

Who has a Cochlear Implant?

Children and Adults of any age can be fitted with, and benefit from a Cochlear Implant. The youngest recipient of an implant was just 5 months old, and there is no upper age for implantation. Adults with post-lingual deafness have had very good experiences of recognising the new senses and relating them to sounds they remember meaning they are comfortable with communication normally, based on using just the device alone. Young children who have pre-lingual deafness generally may need to learn an additional sign language, speech reading, lip-reading or cued speech technique to help them understand the senses that they are feeling.

Children who receive the implant early, and have the correct amount of post implantation therapy can go on to learn speech, a language and social skills. The majority of children who get the implant are between 1 and 5 years old. Children who receive it earlier will be exposed to sounds that are beneficial during the critical period when children learn speech and language skills.

Who can be considered for an implant?

In the UK, Cochlear Implants will be considered for anyone who cannot gain any useful input from hearing aids, and must instead rely solely on lip reading or sign language to communicate. Your family doctor should always be your first contact when looking to discuss this procedure.

Some children who have received implants early in life have had a sufficient benefit from them and had no problem joining mainstream education and living an ordinary life. If you are an adult and  have been advised to look into cochlear implants, you should look for one of the 20 implantation centres across the UK. There, the staff will carry out the necessary tests and predict the benefits that the surgery may bring. As the technology develops, the criteria for deciding whether somebody might be a suitable candidate for a cochlear implant also change.

In the United States, the decision to receive an implant should involve discussions with medical specialists, like in the UK, including an experienced cochlear-implant surgeon. Due to the different healthcare systems between the countries, it can be very expensive for a Cochlear Implant in the US.

A person’s healthcare insurance may or may not cover the expense, so it is worth checking with your healthcare insurer. Some individuals may choose not to have a cochlear implant for a variety of personal reasons. Surgical implantations are almost always safe, although complications are a risk factor, just as with any kind of surgery. Another issue to consider is the post implantation therapy that is needed. The user will have to take time to learn the sounds the implant generates and the senses that the user feels when it is activated and picking up sounds. This process takes time and practice. Speech-language pathologists and audiologists are frequently involved in this learning process. Prior to implantation, all of these factors need to be considered.

What does the future hold for Cochlear Implants?

Technological advances promise to keep this industry developing at an almost alarming rate. Electronic devices will become smaller and cheaper, making them even more accessible to a greater number of people, for a wider number of reasons.

Currently, scientists and University researchers are looking at different uses for the technology, based on studies of users who already have implants. The quality of sound is being researched – sounds will in the future become more like normal hearing by including a higher density and amount of electrodes. Currently, there are around 24 electrodes in a device, but scientists are looking at devices with 240 electrodes. Also, smaller electrode arrays will provide different purpose devices that can be used to target hearing loss in different frequencies – repairing the sense of sound for people who cannot hear high pitched noises.

As previously mentioned, the wholly internal implant is being developed, which will in the long term offer an internal microphone and a lifetime battery. This is some years away, but as technology advances it, in theory, should be possible.

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