Cochlear implants Neurostimulation

cochlear implant

cochlear implants have provided partial hearing more 120,000 persons worldwide of 2008. electrical stimulation used in cochlear implant provide functional hearing in totally deafened persons. cochlear implants include several subsystem components external speech processor , radio frequency (rf) transmission link internal receiver, stimulator, , electrode arrays. modern cochlear implant research started in 1960s , 1970s. in 1961, crude single electrode device implanted in 2 deaf patients , useful hearing electric stimulation reported. first fda approved complete single channel device released in 1984. in cochlear implants, sound picked microphone , transmitted behind-the-ear external processor converted digital data. digitized data modulated on radio frequency signal , transmitted antenna inside headpiece. data , power carrier transmitted through pair of coupled coils hermetically sealed internal unit. extracting power , demodulating data, electric current commands sent cochlea stimulate auditory nerve through microelectrodes. key point internal unit not have battery , should able extract required energy. reduce infection, data transmitted wirelessly along power. inductively coupled coils best candidate power , data telemetry. parameters needed internal unit include pulse amplitude, pulse duration, pulse gap, active electrode, , return electrode used define biphasic pulse , stimulation mode. example of commercial devices include nucleus 22 device utilized carrier frequency of 2.5 mhz , later in newer revision called nucleus 24 device, carrier frequency increased 5 mhz. internal unit in cochlear implants asic (application-specific integrated circuit) chip responsible ensure safe , reliable electric stimulation. inside asic chip, there forward pathway, backward pathway, , control units. forward pathway recovers digital information rf signal includes stimulation parameters , handshaking bits reduce communication error. backward pathway includes telemetry voltage

sampler reads voltage on period of time on recording electrode. stimulator block responsible deliver predetermined current external unit microelectrodes. block includes reference current , digital analog converter transform digital commands analog current.