Cochlear Implants: Helping the Deaf to Hear
What is Hearing?
The outer ear detects sound, which is the vibration of the air causedby anything from a person speaking to a CD player making music. Thesound then travels down the ear canal to the ear drum, a thin, coned shaped piece of skin about .4 inches in diameter. The ear drum vibrates when sound impacts it. The vibrations are transmitted to a series of bones in the middle ear, known as the malleus, the incus, and the stapes. These bones in turn transmit sound vibrations to the fluidfilled cochlea or inner ear.
Inside the cochlea, the basilar membrane, is a rigid surface that extends across its length. When the stapes moves in and out, itpushesand pulls on the basilar membrane. This force starts a wave moving along the surface of the membrane. The wave travels something like ripples along the surface of a pond, moving from the oval window down to the other end of the cochlea. The basilar membrane has a peculiar structure, made of 20,000 to 30,000 reed-like fibers thatextend across the width of the cochlea. A specific wave frequency will resonate perfectly with the fibers at a certain point, causing them to vibrate rapidly.
The organ of corti is a structure containing thousands of tiny hair cells. It lies on the surface of the basilar membrane and extends across the length of the cochlea. The wave energy in the basilar membrane is strong enough to move the organ of corti hair cells.When these hair cells are moved, they send an electrical impulse through the cochlear nerve. The cochlear nerve sends these impulses onto the cerebral cortex, where the brain interprets them.
What is Hearing Loss?
For ninety five percent of people with severe hearing loss, the problem occurs when the tiny structures in the inner ear such as the corti hair cells wear down or get damaged. Sound enters the inner ear, but does not get transmitted to the brain properly,�¯�¿�½ This kind o fnerve deafness can be caused by loud noise, use of ear-damaging orototoxic drugs, infections like measles and meningitis, an accident or trauma,or a birth or hereditary defect.
The remaining five percent of hearing problems are due toconductive hearing loss. In these conditions, sound is not transferredfrom the outer to the inner ear.Conductive hearing loss can result froma punctured eardrum, severely impacted ear wax , head trauma, birth defects,or heredity.�¯�¿�½ In otosclerosis, a form of conductive hearing loss, the tinybones of the inner ear become stiffened and no longer transmit soundproperly. Surgery can help some people with otosclerosis.
Treating Hearing Loss
For many people with nerve hearing loss, use of a hearing aid can bring great benefit. The hearing aid amplifies sound enough to overcome the damage in the inner ear. But for some people with severe deafness,a cochlear implant can work wonders.
What is a cochlear implant?
A cochlear implant is a small, complex electronic device that can help to provide a sense of sound to a person who is profoundly deaf or severely hard of hearing. An implant has four basic parts.
The microphone picks up sound and is worn just behind the ear. The speech processor is worn on the body, sometimes just behind the ear with the microphone. Finally, a mall device is placed under the skin, behind the ear, with electrodes inside the cochlea.
A cochlear implant is very different from a hearingaid. Hearing aids amplify sound. Cochlear implants compensate for damaged or non-working parts of the inner ear. When hearing is functioning normally, complicated parts of the inner ear convert soundwaves in the air into electrical impulses. These impulses are then sent to the brain, where a hearing person recognizes them as sound. A cochlear implant works in a similar manner. It electronically finds useful sounds and then sends them to the brain.
More modern versions of�¯�¿�½ the cochlear implant actual have the ability to directly connect with devices like CD players, televisions, and computers which, along with sound processing software, can help a person listen to sounds such a music witha greater appreciation.
Who Gets Cochlear Implants?
Some sixty thousand people, including almost twenty five thousand in the UnitedStates, have received cochlear implants. The most famous person to have received a cochlear implant is radio talk show host RushLimbaugh.
Adults who have lost all or most of their hearing in later life can often benefit from cochlear implants. These older candidates can often associate the sounds made through an implant with sounds they remember.�¯�¿�½
Young children, particularly those whose nerve deafness is hereditary, can also be candidates for implants. Cochlear implants, coupled with intensive post-implantation therapy, can help young children to acquire speech and language skills hey would otherwise not have. The best age for implantation is still a matter for debate, but most children who receive implants are between 2and 6 years old.
Receiving a Cochlear Implant
The installation of a cochlear implant is a surgical procedure and, as with all such procedures, carries with it a small element of risk. Also, a person receiving a cochlear implant will undergo a period in which he or she will have to learn to interpret sounds created by the implant. Tuning of the system and adjusting the software will also be necessary. Not everyone acquires as much hearing as one might like. The procedure is also very expensive. These are considerations one should discuss with ones medical provider before making the decision to get the cochlear implant.
The Future of Cochlear Implants
The technology of cochlear implants is changing rapidly. The potential of even greater improvement for people who have already had implants installed is very real. And more and more people are becoming candidates for the implant.
