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Health and Disease

Cochlear Implants: A Success Story For Auditory Prosthesis

As one of the many success stories of medical prostheses, cochlear implants are capable of providing a sense of hearing through electrical stimulation.

Introduction

A cochlear implant is an electronic device that is surgically implanted to treat patients that are profoundly deaf. The first cochlear implant devices, invented by William House and John Doyle, were given to patients in 1961 (Turkington). Despite mixed results, the devices were the first successful auditory prosthesis, and they presented an interesting possibility: the ability to restore the human sense of hearing through electrical stimulation. Now, though modern cochlear implant devices have evolved from those first used in 1961, that possibility has turned into a reality. With technological advancements, cochlear implants have resulted in more viable hearing for patients. According to the National Institute on Deafness and Other Communication Disorders, 96,000 people in the US and 324,200 people worldwide have received cochlear implants as of 2017 (Turkington).

A cochlear implant is a viable option for patients who have sensorineural hearing loss—hearing loss due to damage to the sensory hair cells in a part of the inner ear called the cochlea. Movement of hair cells stimulates nerve cells (ganglion cells), which carry an electrical current to the auditory nerve that, in turn, sends the signals to the brain. In sensorineural hearing loss, however, sounds do not make it to the auditory nerve or to the brain, where the electrical signals are interpreted as sound, due to damaged hair cells. Cochlear implants combat this issue, and, while they cannot fully restore hearing, they allow patients to sufficiently hear and understand speech (Turkington).

How do cochlear implants work?

Figure: Diagram showing the external and internal parts of a cochlear implant (Diagram of Cochlear Implant).

A cochlear implant contains external parts (worn on the outside of the ear) and internal parts, which are surgically implanted in the patient, underneath the skin. The external parts (a microphone, speech processor, and transmitter) are responsible for collecting and sending sounds to the internal parts. The microphone receives sound from the environment, which is converted into a digital signal by the speech processor; this signal includes information about the sound received, such as pitch, loudness, and timing. The digital signals are converted into FM radio signals and sent to the internal parts of the cochlear implant by the transmitter (Turkington).

The signals reach the internal parts, which are implanted through an outpatient procedure for adult and adolescent patients and a one-night stay at the hospital for children. The area behind a patient’s ear is first shaved or the hair is sterilized. An incision is then made that opens the mastoid bone, allowing a device called the receiver-simulator to be placed in a depression in the bone before being sutured (stitched). The receiver-simulator receives the FM radio signals sent by the transmitter and converts them to electrical signals. The next step in the surgical procedure is threading the electrodes through the cochlea so that electrodes are positioned closely to the ganglion cells. The receiver-simulator and the electrodes that are in the cochlea are connected by a wire. These electrodes take on the job of stimulating the ganglion cells that transmit signals to the auditory nerve, which hair cells are normally responsible for. This increased nervous response to sound allows the electrical signal to reach the brain (Turkington). The resulting sounds from the implant are more artificial and mechanical than natural sounds, but they allow for improved sound detection and speech understanding.

Benefits

The results of cochlear implants vary, but the most optimal result is a near normal ability to understand speech. They improve a patient’s ability to talk on the phone, lip-read, watch TV with facial cues, and listen to music. They also help differentiate between the type and volume of sounds; patients may better perceive loud, medium, and soft sounds, such as the slamming of doors, ringing of phones, or rustling of leaves. Additionally, cochlear implants can improve a patient’s speech by regulating it so that it is easier to understand (Turkington). 

Risks

Cochlear implants have risks associated with the surgical implant procedure, as surgery with general anesthesia is needed for the implant. Some of these risks are injury to the facial nerve, cerebrospinal and perilymph fluid leak, meningitis, infection, and ringing and numbness around the ear, among others. There is also the risk of the implant failing if it’s rejected by the body, which results in the need for another surgical procedure and, possibly, localized inflammation (“Benefits and Risks of Cochlear Implants”). However, the failure rates of cochlear implants are generally low; around 0.2% of patients reject the implant, and 0.5% require reimplantation (“Cochlear Implants”).

Conclusion

To those with sensorineural hearing loss, cochlear implants are a viable option that restores a sense of hearing for patients. As with any other surgical procedure, there are a number of risks, but cochlear implants are generally one of the safer procedures for medical prosthesis. They hold the potential to restore patients to near normal hearing with benefits in speech and sound reception. While they produce “mechanical” sounds and are not capable of fully restoring a patient’s hearing, cochlear implants represent the progress and potential of medical prosthesis in restoring the human body and even the human senses.

Michelle Li, Youth Medical Journal 2020

References

“Benefits and Risks of Cochlear Implants.” U.S. Food and Drug Administration, http://www.fda.gov/medical-devices/cochlear-implants/benefits-and-risks-cochlear-implants. Accessed 29 Nov. 2020.

“Cochlear Implants.” Hearing Link, http://www.hearinglink.org/your-hearing/implants/cochlear-implants/. Accessed 24 Nov. 2020.

Diagram of Cochlear Implant. Mayo Clinic, http://www.mayoclinic.org/medical-professionals/pediatrics/news/cochlear-implants-early-intervention-to-optimize-language-outcomes/mac-20452729. Accessed 29 Nov. 2020.

“Modern Cochlear Implant.” Albert and Mary Lasker Foundation, http://www.laskerfoundation.org/awards/show/modern-cochlear-implant/. Accessed 29 Nov. 2020.Turkington, Carol A., and Josephine S. Campbell. “Cochlear Implants.” The Gale Encyclopedia of Surgery and Medical Tests, edited by Deirdre S. Hiam, 4th ed., vol. 1, Gale, 2020, pp. 383-88. Gale Health and Wellness, link.gale.com/apps/doc/CX7980900121/HWRC?u=mlin_m_newtnsh&sid=HWRC&xid=90ed2e06. Accessed 29 Nov. 2020.

Turkington, Carol A., and Josephine S. Campbell. “Cochlear Implants.” The Gale Encyclopedia of Surgery and Medical Tests, edited by Deirdre S. Hiam, 4th ed., vol. 1, Gale, 2020, pp. 383-88. Gale Health and Wellness, link.gale.com/apps/doc/CX7980900121/HWRC?u=mlin_m_newtnsh&sid=HWRC&xid=90ed2e06. Accessed 29 Nov. 2020.

By Michelle Li

Michelle Li is a high school junior in Massachusetts. She hopes to pursue medicine in the future and is especially interested in pediatrics.

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