Abstract
Cochlear implants are the treatment of choice for the auditory rehabilitation of patients with sensory deafness. They restore the missing function of inner hair cells by transforming the acoustic signal into electrical stimuli for activation of auditory nerve fibers. Due to the very fast technology development cochlear implants provide open-set speech understanding in the majority of patients including the use of the telephone. Children can achieve a near to normal speech and language development provided their deafness is detected early after onset and implantation is performed quickly thereafter. The diagnostic procedure as well as the surgical techniques have been standardized and can be adapted to the individual anatomical and physiological needs both in children and adults. Special cases such as cochlear obliteration or malformations can be addressed. Device failures and medical complications might require special measures and reimplantation which can be done in most cases in a straight forward way. Technology upgrades count for better performance.Future developments will focus on better electrode nerve interfaces by improving electrode technology. An increased number of electrical contacts as well as the biological treatment with regeneration of the dendrides growing onto the electrode will increase the number of electrical channels. This will give room for improved speech coding strategies in order to create the bionic ear, i. e. to restore the process of natural hearing by means of technology. The robot assisted surgery will allow for high precision surgery and reliable hearing preservation. Biological therapies will support the bionic ear. Methods are biohybrid electrodes which are coded by stem cells transplanted into the inner ear to enhance autoproduction of neurotrophins. Local drug delivery will focus on suppression of trauma reaction and local regeneration. Gene therapy by nanoparticles will hopefully lead to the preservation of residual hearing in patients being affected by genetic hearing loss. Overall the cochlear implant is a very powerful tool to rehabilitate patients with sensory deafness. More than 1 million of candidates in Germany today could benefit from this high technology auditory implant. Only 50,000 are implanted so far. In the future the procedure can be done under local anesthesia, will be minimal invasive and straight forward. Hearing preservation will be routine.
Highlights
Introduction and basics1.1 Principle of cochlear implantCochlear implants are electrical prostheses that trigger auditory sensations via a direct electrical stimulation of the hearing nerve
The intracochlear position of the electrode allows for a differentiated stimulation of the hearing nerves and the transmission of different perceptions of pitches. This simulation of the frequency organization of the inner ear leads to the fact that complex sound signals such as speech are transformed into a differentiated neuronal stimulation pattern of the hearing nerve, which is the base for speech understanding with a cochlear implant
Lenarz: Cochlear implant – state of the art Table 1: Preoperative diagnostics for indication of cochlear implantation in adult (A) and pediatric (P) patients and section planes so that for example all 4 nerves may be identified in the internal auditory meatus (Figure 9)
Summary
Cochlear implants are electronical stimulus prostheses for the functional replacement of the inner ear. The intracochlear position of the electrode allows for a differentiated stimulation of the hearing nerves and the transmission of different perceptions of pitches This simulation of the frequency organization of the inner ear leads to the fact that complex sound signals such as speech are transformed into a differentiated neuronal stimulation pattern of the hearing nerve, which is the base for speech understanding with a cochlear implant. By surface functionalization and additional biological therapies, the regeneration of the hearing nerves with dendrites growing onto the electrode as well as avoiding further degeneration of spiral ganglia cells will be achieved This may lead to significantly better speech processing strategies that even allow for a tonal hearing, for example of music. Implantable hearing systems are currently developed and will make possible the so-called invisible hearing to overcome the stigma of hearing impairment
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