Juan Scheepers – Cochlear Implant

A cochlear implant (CI) is a surgically implanted electronic device that provides 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 hearing aids, the cochlear implant does not amplify sound, but works by directly stimulating any functioning auditory nerves inside the cochlea with an electric field.

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

External:

• a microphone which picks up sound from the environment

• a speech processor which selectively filters sound to prioritize audible speech and sends the electrical sound signals through a thin cable to the transmitter,

• a transmitter, which is a coil held in position by a magnet placed behind the external ear, and transmits the processed sound signals to the internal device by electromagnetic induction,

Internal:

The internal part of a cochlear implant (model Cochlear Freedom 24 RE)

• 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 to the nerves in the scala tympani and then directly to the brain through the auditory nerve system. There are 4 manufacturers for Cochlear implants, and each one produces a different implant with a different number of electrodes. Advanced Bionics produces implants with 16 electrodes and use a technique called current steering in which two electrodes are stimulated simultaneously with different current levels to produce intermediate virtual channels. The number of channels is not a primary factor upon which a manufacturer is chosen; the signal processing algorithm is also another important block.

A secondary coil is implanted beneath the skull’s skin and inductively coupled to the primary headpiece coil. The headpiece coil has a magnet by which it attaches to another magnet placed on the secondary coil often beside the cochlear implant. The implant relays the incoming signal to the implanted electrodes in the cochlea. The speech processor allows an individual to adjust the sensitivity of the device. The implant gives recipients additional auditory information, which may include sound discrimination fine enough to understand speech in quiet environments. Post-implantation rehabilitative therapy is often critical to ensuring successful outcomes.

As of 2009, approximately 150,000 people worldwide had received cochlear implants; in the United States, about 30,000 adults and over 30,000 children are recipients. The vast majority are in developed countries due to the high cost of the device, surgery and post-implantation therapy. A small but growing segment of recipients have bilateral implants (one implant in each cochlea).