I have a son four years old with hearing loss. I was advised to do cochlear implantation. Can you explain this procedure and advise me where is the best place to do this sort of operation?

Y.

Cochlear implantation was one of the two major advances in hearing technology achieved in the latter half of the 20th century. (Digital hearing aids were the second major advance.) Thanks to cochlear implants, individuals too deaf to use hearing aids can nevertheless be "aided." To explain cochlear implantation, I need to give you some background on what the cochlea is, and how it works. First you might want to read another article I wrote about how sound energy works its way to the inner ear.

The cochlea is the organ responsible for hearing. It's a fluid-filled spiral tube in the inner ear that's filled with rows of hair cells. That's just their name -- hair cells are about as different from the hair on your head as you can imagine.

A pressure wave of sound stimulates the hair cells, essentially by deflecting the hair-like projections that extend from the end of each cell; in response to this stimulation, the hair cell emits an electrochemical signal. The hair cells are neurosensory cells, cells that emit nervous impulses in response to sensation. Other examples of neurosensory cells are the taste buds, the rods and cones in the retina of the eye, and the pain-, pressure- and temperature-receptor cells of skin.

These nervous impulses (the electrochemical signals) from the hair cells in turn stimulate the auditory nerve. Nerves are composed of multiple cells called neurons. To understand what nerves are like, imagine holding in your hand 100 straight noodles. The collected bundle of noodles -- what you hold in your fist -- is the nerve; the individual noodles are neurons. The auditory nerve emanates from the central core of the cochlea and travels to a structure near the base of the brain called the brainstem. Within an area of the brainstem called the cochlear nucleus, these cochlear neurons pass their information on to other neurons, which then relay the information to higher portions of the brain.

In many forms of deafness, the hair cells are devastated, but the auditory nerve and all other parts of the auditory system are still in good shape. THAT's the purpose of a cochlear implant: It directly stimulates the auditory nerve, bypassing severely damaged hair cells. In the cochlear-implantation procedure, an electrode (a device that conducts electricity) is threaded through the middle ear into the cochlea.

It is extremely important to understand that the cochlear implant does NOT automatically restore hearing. Instead, it "translates" sound into a pattern that is relayed to the brain. It is up to the brain to translate this pattern back into information that is recognizable as speech, music, environmental noise and so forth.

Very young children can perform this translation automatically. Older children have greater difficulty acquiring this ability, and adults have an even harder time learning. Thus, following the implantation surgery, intensive training with an audiologist (a professional who specializes in the testing of hearing) who is highly skilled in this form of training is absolutely essential.

Please note that cochlear implants are radically different from the assistance provided by hearing aids, which are (relatively speaking) simple devices that amplify sound.

The cochlear-implantation operation and postoperative training are both highly specialized skills that are not widely available. You need to take your son to a medical center that specializes in this procedure, and you may very well have to do a bit of traveling.