In the late 1950s, researchers began to wonder if it would be possible to replace the electrical signals from hair cells that were missing in people with sensorineural hearing loss, especially in most people who had auditory nerves intact. The effort of the researchers to create a cochlear implant had to face skepticism and discouraging technical obstacles. The development of the implants has considerably improved making them more comfortable and easier to use over time and not only in the auricular area, but also with the Tijuana dental implants.
But they were fortunate to begin at a time when there was a lot of knowledge about the electrical signals produced by the organ of Corti that were transmitted to the auditory nerve. The auditory system could organize sounds into 24 channels. Thanks to the experiments with animals it was known that the organ of Corti and the auditory nerve were at the base of this organization and that the fibers of a part of the nerve transported information about the tones low, the fibers of the next part carried information on slightly higher tones and so on predictably.
However, the preliminary experimental implants did not take advantage of the tonotopic organization of the cochlea. Several groups of researchers began implanting single-channel electrodes within the cochlea of deaf volunteers. Both researchers and volunteers knew that these rudimentary devices would not provide enough information to encode speech. Thought that synchronization of electrical discharges from electrodes would allow volunteers to determine the tone of a sound. In fact, the volunteers were able to obtain a large amount of auditory information from the single channel. Although the perception of speech was poor, they could deduce, for example, if a spoken word had one or two syllables, and they perceived slightly the tone of a sound by synchronizing the neural spines; this was enough to serve as an important aid to lip reading.
That surprising success encouraged the researchers. In the early 70’s several groups were working on more sophisticated devices with several electrodes. But how many electrodes would be needed? The auditory nerve contains 30,000 fibers. Would the researchers have to have 30,000 electrodes to stimulate all the nerve fibers individually to be able to simulate intelligible speech sounds? If so, it was clear that the project would not be practical. Further simplified the system after discovering the results of investigations from an unexpected source.
Would an implant of that type be safe? Many doctors and researchers thought that a cochlear implant with several electrodes would be like putting a telephone pole into the cavities of the inner ear and that would probably destroy the delicate cells of the ganglia, which transfer the signals from the hair cells to the brain through the nerve. auditory. The implant did not damage ganglion cells. In fact, the cells were reanimated by stimulation.
The functioning of cochlear implants. The sound picked up by a microphone (1) passes through a cable to a speech processor (2), which is worn on the belt, in a pocket, or in the ear, which converts the signal into electrical impulses. The impulses return through the cable to a transmitter (3) fixed to the head, which in turn sends the coded impulses through the skin to a stimulator-receiver (4 and 5) implanted in the bone just below the transmitter. The stimulator retransmits the signal through a series of tiny wires threaded directly into the cochlea, activating the fibers of the nerves that, in turn, send the signal