Cochlear implants



A cochlear implant is a surgically implanted hearing aid that can help provide a sense of sound to a person who is profoundly deaf or severely hard of hearing. The cochlear implant is often referred to as a bionic ear. Unlike other kinds of hearing aids, the cochlear implant doesn't amplify sound, but works by directly stimulating any functioning auditory nerves inside the cochlea with electrical impulses. External components of the cochlear implant include a microphone, speech processor and transmitter.

An implant does not restore or create normal hearing. Instead, under the appropriate conditions, it can give a deaf person a useful auditory understanding of the environment and help them to understand speech when coupled with post-implantation therapy. According to the United States Food and Drug Administration (2002), approximately 59,000 people worldwide have received cochlear implants; roughly half are children and half adults. The vast majority are in developed countries due to the prohibitive cost of the device, surgery and post-implantation therapy — Mexico had performed only 55 cochlear implant operations by the year 2000 (Berruecos 2000).

Cochlear implants are controversial, and their introduction has seen the renewal of a century-old debate about models of deafness that often has the medical profession on one side and the Deaf community on the other. While cochlear implants have been welcomed by late-deafened adults, hearing parents of deaf children, audiologists, speech pathologists, and surgeons, the implantation of deaf children has been vigorously opposed by many from the signing Deaf community.

History
The discovery that electrical stimulation to the auditory system can create a perception of sound occurred around 1790, when Alessandro Volta (the developer of the electric battery) placed metal rods in his own ears and connected them to a 50-volt circuit, experiencing a jolt and hearing a noise "like a thick boiling soup". Other experiments occurred sporadically, until electrical (sound amplifying) hearing aids began to be developed in earnest the 20th century.

The first direct stimulation of an acoustic nerve with an electrode was performed in the 1950s by the French-Algerian surgeons André Djourno and Charles Eyriès. They placed wires on nerves exposed during an operation, and reported that the patient heard sounds like "a roulette wheel" and "a cricket" when a current was applied.

In 1961, American doctor William House had Djourno's paper translated and had devices made which he implanted into three patients. However, he stopped work on the implants until 1972, by which time some experimental work had begun in California, Paris, Vienna and Melbourne. House's implants used a single active electrode, but results were limited. Throughout the 1970s, Melbourne researcher Graeme Clark developed implants which stimulated the cochlear at several points, and in 1978, Melbourne man Rod Saunders become the first person in the world to receive a multi-channel cochlear implant.

In December 1984, the cochlear implant was approved by the United States Food and Drug Administration to be implanted into adults in the United States. In 1990 the FDA lowered the approved age for implantation to 2 years, then 18 months in 1998, and finally 12 months in 2002, although special approval has been given for babies as young as 6 months.

Throughout the 1990s, the large external components which had been worn strapped to the body grew smaller and smaller thanks to developments in miniature electronics. Today (2006), most school-age children and adults use a small behind-the-ear (BTE) speech processor about the size of a power hearing aid. Younger children have small ears and might mishandle a BTE. Therefore, they often wear the speech processor on their hip in a pack or small harness. The processor is connected by a wire to the microphone and transmitter at ear or head level.

Since hearing in two ears allows people to localize sounds and to hear better in noisy environments, bilateral (both ear) implants are currently being investigated. Users generally report better hearing with two implants, and test show that bilateral implant users are better at localizing sounds and hearing in noise. Nearly 3000 people worldwide are bilateral cochlear implant users, including 1600 children. As of 2006, the world's youngest recipient of a bilateral implant was just over 5 months old (163 days) in Germany (2004).

Parts of the cochlear implant
The implant is surgically placed under the skin behind the ear. The basic parts of the device include:
 * External:


 * a microphone,
 * a speech processor which selectively filters sound to prioritise audible speech and sends the electrical sound signals through a thin cable to the transmitter,
 * a transmitter, which is a magnetic pad placed behind the external ear, and transmits the processed sound signals to the internal device by electromagnetic induction,
 * Internal:


 * a receiver and stimulator secured in bone beneath the skin, which converts the signals into electric impulses and sends them through an internal cable to electrodes,
 * an array of up to 22 electrodes wound through the cochlea, which send the impulses directly into the brain.

Who can use a cochlear implant?
There are a number of factors that determine the degree of success to expect from the operation and the device itself. Cochlear implant centers determine implant candidacy on an individual basis and take into account a person's hearing history, cause of hearing loss, amount of residual hearing, speech recognition ability, health status, and family commitment to aural habilitation/rehabilitation.

A prime candidate is described as:
 * having severe to profound sensorineural hearing impairment in both ears
 * a functioning auditory nerve is present
 * has lived a short amount of time without hearing
 * has good speech, language, and communication skills
 * other kinds of hearing aids are not helping
 * no medical reason to avoid surgery
 * lives in or desires to live in the "hearing world"
 * has realistic expectations about results
 * has the support of family and friends.

Type of hearing impairment
Once a cochlear implant is put in place, any residual hearing a person has in that ear will be destroyed. For this reason, people with mild or moderate sensorineural hearing loss or conductive hearing loss are generally not candidates for cochlear implantation. After the implant is put into place, sound no longer travels via the ear canal and middle ear but will be picked up by a microphone and sent through the device's speech processor to the implant's electrodes inside the cochlea.

The presence of auditory nerve fibres is essential to the functioning of the device: if these are damaged to such an extent that they cannot receive electrical stimuli, the implant will not work. A small number of individuals with severe auditory neuropathy may also benefit from cochlear implants.

Age of recipient
Post-lingually deaf adults and pre-lingually deaf children form two distinct groups of potential users of cochlear implants with different needs and outcomes. Those who have lost their hearing as adults were the first group to find cochlear implants useful, in regaining some comprehension of speech and other sounds. If an individual has been deaf for a long period of time, the brain may begin using the area of the brain normally used for hearing for other functions. If such a person receives a cochlear implant, the sounds can be very disorienting, and the brain often will struggle to readapt to sound.

The risk of surgery in the older patient must be weighed against the improvement in quality of life. As the devices improve, particularly the sound processor hardware and software, the benefit is often judged to be worth the surgical risk, particularly for the newly deaf elderly patient. 

The other group of customers are parents of children born deaf who want to ensure that their children grow up with good spoken language skills. Research shows that congenitally deaf children who receive cochlear implants at a young age (less than 2 years) have better success with them than congenitally deaf children who first receive the implants at a later age, though the critical period for utilizing auditory information does not close completely until adolescence.

The operation, post-implantation therapy and ongoing effects
The device is sugically implanted under a general anaesthetic, and the operation usually takes from 1½ to 5 hours. The patient normally remains in hospital for one day for adults and 1-2 days for children. As with every medical procedure, the surgery involves a certain amount of risk; in this case, the risks include skin infection, onset of tinnitus, damage to the vestibular system, and damage to facial nerves that can cause disfiguring paralysis. The operation also destroys any residual hearing the patient may have; as a result, some doctors advise single-ear implantation, saving the other ear in case a biological treatment becomes available in future.

Results are not immeditate, and post-implantation therapy is required as well as time for the brain to adapt to hearing new sounds. In the case of congenitally deaf children, audiological training and speech therapy continue for years, though implanted infants often have age-appropriate spoken language skills by the time they reach kindergarten. The participation of the child's family in working on spoken language development is considered to be even more important than therapy.

In 2003, the CDC and FDA announced that children with cochlear implants are at an increased risk of bacterial meningitis (Reefhuis 2003). Many users, audiologists, and surgeons also report that when there is an ear infection causing fluid in the middle ear, it can fact affect the cochlear implant, leading to reduced hearing.

The implant has a few effects unrelated to hearing. People who have cochlear implants are cautioned against contact sports because there is some risk of a blow to the head damaging the housing of the internal device. Manufacturers have also cautioned against scuba diving due to the pressures involved, but the depths found in normal recreational diving appear to be safe. The external components must be turned off and removed prior to swimming or showering. The cochlear implant is unsafe in areas with strong magnetic fields, and thus cannot be used with certain diagnostic tests such as magnetic resonance imaging (MRI). The electronic stimulation the implant creates appears to have a positive effect on the nerve tissue that surrounds it.

Cost
In the United States, medical costs run from USD$15,000 to $40,000; this includes evaluation, the surgery itself, hardware (device), and rehabilitation. Some of this can be covered by health insurance. In developed countries with some form of free public health care, the rate of implantation is greater than in the US, as the costs (or some of the costs) are borne by the government. In Australia, Denmark and Norway, 80 to 90% of deaf children have cochlear implants.

Efficacy
A cochlear implant will not "cure" deafness or hearing impairment, but is a prosthetic substitute for hearing. Even after receiving implants and therapy, audiologists find most users to be “severely hearing-impaired” (Osberger and Kessler 1995), or, in some cases, "profoundly hearing impaired" (Miyamoto et al. 1995).

Some patients find them very effective, others somewhat effective, some find them useless and others feel overall worse off with the implant than without. For people already functional in spoken language who lose their hearing, they can be a great help in restoring functional comprehension of speech, especially if they have only lost their hearing for a short time.

British Member of Parliament Jack Ashley received a cochlear implant in 1994 at age 70 after 25 years of deafness, and reported that he has no trouble speaking to people he knows one on one, even on the telephone, although he might have difficulty with a new voice or with a busy conversation, and still had to rely to some extent on lipreading. He described the robotic sound of human voices perceived through the cochlear implant as "a croaking dalek with laryngitis". Even modern cochlear implants have at most 22 electrodes to replace the 16,000 delicate hair cells are used for normal hearing. However, the sound quality delivered by a cochlear implant is often good enough that many users do not have to rely on speech-reading (lipreading).

Adults who have grown up deaf often find the implants ineffective or irritating; whether this is because they are unaccustomed to interpreting sound and would find that difficult even if they were given perfect hearing is unclear.

For small children, there have been mixed results. Almost all children with implants have some "useful" perception of sound, and more children have better sound perception with cochlear implants than without, but for some, the sound they receive is too garbled for them to interpret as language. As a result, those without adequate sign language input often miss out on properly acquiring any language at all in the critical period of early childhood. Some writers have noted that children with cochlear implants are more likely to be educated orally and without access to sign language (Spencer et al 2003).

Ethical issues
Cochlear implants for congentially deaf children are most effective when implanted at a young age, during the critical period in which the brain is still learning to interpret sound; hence they are implanted before the recipients can decide for themselves. Many question the ethics of such invasive elective surgery on healthy children — pointing out that manufacturers and specialists have exaggerated the efficacy and downplayed the risks of a procedure that they stand to gain from.

Much of the strongest objection to cochlear implants has come from the Deaf community, which consists largely of pre-lingually deaf people who use a sign language as their preferred language. Very distinct from adults who have lost their hearing, many do not share the pathological view of deafness held by the medical profession that deafness as a disability to be "fixed", but instead celebrate being Deaf and value their membership of the visual culture that they have grown up in (see Deaf culture). The confict over these opposing models of deafness has raged for hundreds of years, and cochlear implants are the latest in a history of medical interventions promising to turn a deaf child into a hearing child — or, more accurately, a child with a hearing impairment.

Critics argue that the cochlear implant and the subsequent therapy often become the focus of the child's identity, at the expense of a positive Deaf identity and the ease of communication in sign language. Measuring the child's success by their success in hearing and speech will lead to a poor self image as "disabled" (because the implants do not produce perfect hearing) rather than having the healthy self-concept of a proud Deaf. Children with implants are often isolated from other deaf children and from sign language (Spencer 2003), and instead are 'married' to a team of hearing experts for the rest of their life who will monitor his cochlear implant and adjust the speech processor, at great expense.

Cochlear implants have been one of the technological and social factors implicated in the decline of sign languages in the developed world (Johnston 2004); some of the more extreme responses from Deaf activists have labelled the widespread implantation of children as "cultural genocide". As cochlear implants began to be implanted into deaf children in the mid to late 1980s, the Deaf community responded with protests in the US, UK, Germany, Finland, France and Australia. Opposition continues today but in many cases has softened, and as the trend for cochlear implants in children grows, deaf community advocates have tried to counter the "either or" formulation of oralism vs manualism with a "both and" approach; some schools now are successfully integrating cochlear implants with sign language in their educational programs.

Dr. Robert Ruben, an ear nose and throat specialist at Montefiore Hospital in the Bronx, said: "If I had a deaf child, I would implant one ear, leaving the other free in case cures develop that require an intact inner ear. I would bring up that child bilingually. Parents could phase out sign later on if they wanted, but it should not be abandoned until it becomes clear that the child can develop satisfactory oral language. The worst mistake is for parents to neglect the one most important thing — that language of any kind, no matter what kind, must somehow be got into the child soon enough."

How the cochlear implant works
The implant works by using the tonotopic organization of the basilar membrane of the inner ear. "Tonotopic organization" is the way the ear sorts out different frequencies so that our brain can process that information. In a normal ear, sound vibrations in the air lead to resonant vibrations of the basilar membrane inside the cochlea. High-frequency sounds (i.e. high pitched sounds) do not pass very far along the membrane, but low frequency sounds pass farther in. The movement of hair cells, located all along the basilar membrane, creates an electrical disturbance that can be picked up by the surrounding nerve cells. The brain is able to interpret the nerve activity to determine which area of the basilar membrane is resonating, and therefore what sound frequency is being heard.

In individuals with sensorineural hearing loss, hair cells are often fewer in number and damaged. Hair cell loss or absence may be caused by a genetic mutation or an illness such as meningitis. Hair cells may also be destroyed chemically by an ototoxic medication, or simply damaged over time by excessively loud noises. The cochlear implant by-passes the hair cells and stimulates the cochlear nerves directly using electrical impulses. This allows the brain to interpret the frequency of sound as it would if the hair cells of the basilar membrane were functioning properly (see above).

Processing
Sound received by the microphone must be processed to determine how the electrodes should be activated. The simplest way of processing would be to divide the acoustic signal by the number of electrodes in the device and apply the resulting voltage to the appropriate electrode. More sophisticated processing algorithms are used in practice because applying voltage to each of the electrodes at the same time would cause currents to flow between the electrodes, which would stimulate the nerves in undesirable ways.

Waveform processing strategies use bandpass filters to divide the signal into different frequency bands. The algorithm chooses a number of the strongest outputs from the filters. The number depends on the algorithm. These strategies emphasize transmission of the temporal aspects of speech.

Feature extraction strategies use features which are common to all vowels. Each vowel has a fundamental frequency (the lowest frequency peak) and formants (peaks with higher frequencies). The pattern of the fundamental and formant frequencies is specific for different vowel sounds. These algorithms try to recognise the vowel and then emphasise its features. These strategies emphasize the transmission of spectral aspects of speech. Feature extraction strategies are no longer widely used.

Transmitter
This is used to transmit the processed sound information over a radio frequency link to the internal portion of the device. Radio frequency is used so that no physical connection is needed, which reduces the chance of infection. The transmitter attaches to the receiver using a magnet that holds through the skin.

Receiver
This component receives directions from the speech processor by way of radio waves sent from the transmitter. (The transmitter also receives its power through the transmission.) The receiver is also a sophisticated mini computer that translates the processed sound information and controls the electrical current sent to the electrodes in the cochlea. It is embedded in the skull behind the ear.

Electrode array
The electrode array is made from a type of silicone rubber, while the electrodes are platinum or a similarly highly conductive material. It is connected to the internal receiver on one end and inserted into the cochlea deeper in the skull. (The cochlea winds its way around the auditory nerve, which is tonotopically organized just as the basilar membrane is). When an electrical current is routed to an intracochlea electrode, an electrical field is generated and auditory nerve fibers are stimulated.

Programming the speech processor
The cochlear implant must be programmed individually for each user. The programming is performed by an audiologist trained to work with cochlear implants. The audiologist sets the minimum and maximum current level outputs for each electrode in the array based on the user's reports of loudness. The audiologist also selects the appropriate speech processing strategy and program parameters for the user.

Manufacurers
Currently (as of 2005), the top three cochlear implant devices are manufacted by Cochlear Corporation, Australia, Advanced Bionics, United States, and MED-EL, Austria. These are similar devices. Each manufacturer has adapted some of the successful innovations of the other companies to their own devices. There is no clear-cut consensus that any one of these implants is superior to the others. Users of all three devices display a wide range of performance after implantation.

Since the devices have a similar range of outcomes, other criteria are often considered when choosing a cochlear implant: usability of external components, cosmetic factors, battery life, reliability of the internal and external components, customer service from the manufacturer, the familiarity of the user's surgeon and audiologist with the particular device, and anatomical concerns.

Cochlear implant in popular culture
In 2000, an Academy Award nominated film Sound and Fury depicted this cultural divide. The Artinian family themselves are a "microcosm" of the deaf culture war and two children – Peter (11 months old) and Heather (7 yrs old) – are caught in the middle.

Two years after the film's release, in September 2002, Heather Artinian got a cochlear implant. Her mother, Nita, got one a few months later.

Famous recipients of cochlear implants include British MP Jack Ashley, conservative U.S. talk-show host Rush Limbaugh, British designer and typographer Tony Malone and Heather Whitestone, Miss America 1995.