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. In 1969, with the help of Jack Urban, House created the first wearable cochlear implant. House's technology used a single electrode and was designed to aid lip-reading. Throughout the 1970s, Melbourne, Australia, researcher Professor Graeme Clark developed implants which stimulated the cochlea at multiple points, and in 1978, Melbourne resident Rod Saunders become the first person in the world to receive a multi-channel cochlear implant.
In December 1984, the Australian 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 in the United States and 4 months internationally.
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).