cochlear implant cochlear implant a cochlear implant (ci) is a surgically implanted neuroprosthesis that provides a person who has moderate-to-profound sensorineural hearing loss with sound perception. with the help of therapy, cochlear implants may allow for improved speech understanding in both quiet and noisy environments. a ci bypasses acoustic hearing by direct electrical stimulation of the auditory nerve. through everyday listening and auditory training, cochlear implants allow both children and adults to learn to interpret those signals as speech and sound. cochlear implantdiagram of a cochlear implant the implant has two main components. the outside component is generally worn behind the ear, but could also be attached to clothing, for example, in young children. this component, the sound processor, contains microphones, electronics that include digital signal processor (dsp) chips, battery, and a coil that transmits a signal to the implant across the skin. the inside component, the actual implant, has a coil to receive signals, electronics, and an array of electrodes which is placed into the cochlea, which stimulate the cochlear nerve. the surgical procedure is performed under general anesthesia. surgical risks are minimal and most individuals will undergo outpatient surgery and go home the same day. however, some individuals will experience dizziness, and on rare occasions, tinnitus or facial nerve bruising. from the early days of implants in the 1970s and the 1980s, speech perception via an implant has steadily increased. more than 200,000 people in the united states had received a ci through 2019. many users of modern implants gain reasonable to good hearing and speech perception skills post-implantation, especially when combined with lipreading. one of the challenges that remain with these implants is that hearing and speech understanding skills after implantation show a wide range of variation across individual implant users. factors such as age of implantation, parental involvement and education level, duration and cause of hearing loss, how the implant is situated in the cochlea, the overall health of the cochlear nerve, but also individual capabilities of re-learning are considered to contribute to this variation. history 1994 body-worn cochlear spectra processor. early cochlear implant users utilized body-worn processors like this one cochlear implant recipient utilizing a behind-the-ear processor (sonnet) andré djourno and charles eyriès invented the original cochlear implant in 1957. this original design distributed stimulation using a single channel. william house also invented a cochlear implant in 1961. in 1964, blair simmons and robert j. white implanted a single-channel electrode in a patient's cochlea at stanford university. however, research indicated that these single-channel cochlear implants were of limited usefulness because they cannot stimulate different areas of the cochlea at different times to allow differentiation between low and mid to high frequencies as required for detecting speech. nasa engineer adam kissiah started working in the mid-1970s on what would become the modern cochlear implant. kissiah used his knowledge learned while working as an electronics instrumentation engineer at nasa. this work took place over three years, when kissiah would spend his lunch breaks and evenings in kennedy's technical library, studying the impact of engineering principles on the inner ear. in 1977, nasa helped kissiah obtain a patent for the cochlear implant; kissiah later sold the patent rights. the modern multi-channel cochlear implant was independently developed and commercialized by two separate teams—one led by graeme clark in australia and another by ingeborg hochmair and her future husband, erwin hochmair in austria, with the hochmairs' device first implanted in a person in december 1977 and clark's in august 1978. parts cochlear implants bypass most of the peripheral auditory system which receives sound and converts that sound into movements of hair cells in the cochlea; the deflection of stereocilia causes an influx of potassium ions into the hair cells, and the depolarisation in turn stimulates calcium influx, which increases release of the neurotransmitter, glutamate. excitation of the cochlear nerve by the neurotransmitter sends signals to the brain, which creates the experience of sound. with an implant, instead, the devices pick up sound and digitize it, convert that digitized sound into electrical signals, and transmit those signals to electrodes embedded in the cochlea. the electrodes electrically stimulate the cochlear nerve, causing it to send signals to the brain. there are several systems available, but generally they have the following components: external: one or more microphones that pick up sound from the environment a speech processor which selectively filters sound to prioritize audible speech a transmitter that sends power and the processed sound signals across the skin to the internal device by radio frequency transmission internal: a receiver/stimulator, which receives signals from the speech processor and converts them into electric impulses an electrode array embedded in the cochlea a totally implantable cochlear implant (tici) is currently in development. this new type of cochlear implant incorporates all the current external components of an audio processor into the internal implant. the lack of external components makes the implant invisible from the outside and also means it is less likely to be damaged or break. assistive listening devices most modern cochlear implants can be used with a range of assistive listening devices (alds), which help people to hear better in challenging listening situations. these situations could include talking on the phone, watching tv or listening to a speaker or teacher. with an ald, the sound from devices including mobile phones or from an external microphone is sent to the audio processor directly, rather than being picked up by the audio processor's microphone. this direct transmission improves the sound quality for the user, making it easier to talk on the phone or stream music. alds come in many forms, such as neckloops, pens, and specialist battery pack covers. modern alds are usually able to receive sound from any bluetooth device, including phones and computers, before transmitting it wirelessly to the audio processor. most cochlear implants are also compatible with older ald technology, such as a telecoil. surgical procedure surgical techniques implantation of children and adults can be done safely with few surgical complications and most individuals will undergo outpatient surgery and go home the same day. occasionally, the very young, the very old, or patients with a significant number of medical diseases at once may remain for overnight observation in the hospital. the procedure can be performed in an ambulatory surgery center in healthy individuals. the surgical procedure most often used to implant the device is called mastoidectomy with facial recess approach (mfra). the procedure is usually done under general anesthesia. complications of the procedure are rare, but include mastoiditis, otitis media (acute or with effusion), shifting of the implanted device requiring a second procedure, damage to the facial nerve, damage to the chorda tympani, and wound infections. cochlear implantation surgery is considered a clean procedure with an infection rate of less than 3%. guidelines suggest that routine prophylactic antibiotics are not required. however, the potential cost of a postoperative infection is high (including the possibility of implant loss); therefore, a single preoperative intravenous injection of antibiotics is recommended. the rate of complications is about 12% for minor complications and 3% for major complications; major complications include infections, facial paralysis, and device failure. although up to 20 new cases of post-ci bacterial meningitis occur annually worldwide, data demonstrates a reducing incidence. to avoid the risk of bacterial meningitis, the cdc recommends that adults and children undergoing ci receive age-appropriate vaccines that generate antibodies to streptococcus pneumoniae. the rate of transient facial nerve palsy is estimated to be approximately 1%. device failure requiring reimplantation is estimated to occur 2.5–6% of the time. up to one-third of people experience disequilibrium, vertigo, or vestibular weakness lasting more than one week after the procedure; in people under 70 these symptoms generally resolve over weeks to months, but in people over 70 the problems tend to persist. in the past, cochlear implants were only approved for people who were deaf in both ears; as of 2014 a cochlear implant had been used experimentally in some people who had acquired deafness in one ear after they had learned how to speak, and none who were deaf in one ear from birth; clinical studies as of 2014 had been too small to draw generalizations. alternative surgical technique other approaches, such as going through the suprameatal triangle, are used. a systematic literature review published in 2016 found that studies comparing the two approaches were generally small, not randomized, and retrospective so were not useful for making generalizations; it is not known which approach is safer or more effective. endoscopic cochlear implantation with the increased utilization of endoscopic ear surgery as popularized by professor tarabichi, there have been multiple published reports on the use of endoscopic technique in cochlear implant surgery. however, this has been motivated by marketing and there is clear indication of increased morbidity associated with this technique as reported by the pioneer of endoscopic ear surgery. complications of cochlear implant surgery as cochlear implant surgical techniques have advanced over the last four decades, the global complication rate for ci surgery in both children and adults has decreased from >35% in 1991 to less than 10% at present. the risk of postoperative facial nerve injury has also decreased over the last several decades to less than 1%, most of which demonstrated complete return of function within six months. the rate of permanent paralysis is approximately 1 per 1,000 surgeries and likely less than that in experienced ci centers. the majority of complications following ci surgery are minor requiring only conservative medical management or prolongation of hospital stay. less than 5% of all complications are major resulting in surgical intervention or readmission to the hospital. reported rates of revision cochlear implant surgery vary in adults and children from 3.8% to 8% with the most common indications being device failure, infection, and migration of the implant or electrode. disequilibrium and vertigo after ci surgery can occur but the symptoms tend to be mild and short-lived. ci rarely results in significant or persistent adverse effects on the vestibular system when hearing conservation surgical techniques are practiced. moreover, gait and postural stability may actually improve post-implantation. outcomes cochlear implant outcomes can be measured using speech recognition ability and functional improvements measured using patient reported outcome measures. while the degree of improvement after cochlear plantation may vary, the majority of patients who receive cochlear implants demonstrate a significant improvement in speech recognition ability compared to their preoperative condition. multiple meta-analyses of the literature from 2018 showed that ci users have large improvements in quality of life after cochlear implantation. this improvement occurs in many different facets of life that extends beyond communication including improved ability to engage in social activities; decreased mental effort from listening; and improved environmental sound awareness. deaf adolescents with cochlear implants attending mainstream educational settings report high levels of scholastic self-esteem, friendship self-esteem, and global self-esteem. they also tend to hold mostly positive attitudes towards their cochlear implants, and as a part of their identity, a majority either do "not really think about" their hearing loss, or are "proud of it." though advancements in cochlear implant technology have helped patients in their understanding of language, users are still unable to understand suprasegmental portions of language, which includes pitch. a study by johns hopkins university determined that for a three-year-old child who receives them, cochlear implants can save $30,000 to $50,000 in special-education costs for elementary and secondary schools as the child is more likely to be mainstreamed in school and thus use fewer support services than similarly deaf children. efficacy a 2019 study found that bilateral cochlear implantation was widely regarded as the most beneficial hearing intervention for acceptable candidates, although it is more likely to be performed and reimbursed in children than adults. the study also found that the efficacy of bilateral implantation could be improved by enhancing communication between the two implants and by developing sound coding strategies specifically for bilateral users. early research reviews found that the ability to communicate in spoken language was better the earlier the implantation was performed. the reviews also found that, overall, while cochlear implants provide open-set speech understanding for the majority of implanted profoundly hearing-impaired children, it was not possible to accurately predict the specific outcome of the given implanted child. research since then has reported long-term socio-economic benefits for children as well