The cochlear implant: historical aspects and future prospects

Abstract

The cochlear implant (CI) is the first effective treatment for deafness and severe losses in hearing. As such, the CI is now widely regarded as one of the great advances in modern medicine. This article reviews the key events and discoveries that led up to the current CI systems, and we review and present some among the many possibilities for further improvements in device design and performance. The past achievements include: (1) development of reliable devices that can be used over the lifetime of a patient; (2) development of arrays of implanted electrodes that can stimulate more than one site in the cochlea; and (3) progressive and large improvements in sound processing strategies for CIs. In addition, cooperation between research organizations and companies greatly accelerated the widespread availability and use of safe and effective devices. Possibilities for the future include: (1) use of otoprotective drugs; (2) further improvements in electrode designs and placements; (3) further improvements in sound processing strategies; (4) use of stem cells to replace lost sensory hair cells and neural structures in the cochlea; (5) gene therapy; (6) further reductions in the trauma caused by insertions of electrodes and other manipulations during implant surgeries; and (7) optical rather electrical stimulation of the auditory nerve. Each of these possibilities is the subject of active research. Although great progress has been made to date in the development of the CI, including the first substantial restoration of a human sense, much more progress seems likely and certainly would not be a surprise.

Fig 1

The cochlear implant designed by Michelson in 1978. a) The internal portion of the device measuring 70 mm in length; b) Radiographic image of a skull with an implant in place, c) The internal portion of the implant, d) The external portion of the implant. (Courtesy of the American Academy of Otolaryngology-Head and Neck Surgery Foundation

Fig 2

The 3M Cochlear implant system developed by House in 1973. Left image) The internal and external portions of the device, Right image) External portion of the device placed on the patient head.(Courtesy of the American Academy of Otolaryngology-Head and Neck Surgery Foundation)

Fig 3

Figure drawn by Chouard in 1973 representing the multiple cochleostomies performed on the promontory of the cochlea from the aspect of the middle ear. Structures are labeled: facial nerve (middle ear segment- (VII 2); Internal carotid artery- (C); Geniculate ganglion- (Gg); Basal turn of Cochlea- (I); Second turn of Cochlea- (II). Courtesy of PR Chouard

Fig 4

The success of the cochlear implant was a worldwide mission. Some important influences are depicted above, with years representing the time of first cochlear implantation and/or the time period of significant research contributions. Some of the major companies which later originated from the early works of each team are also depicted in red.

Fig 5

Photograph of cryo-histological sectioned surfaces from two fresh temporal bones that underwent cochlear implantation. a) Grade 0- with no macroscopic damage; b) Grade 4- where a fracture of osseous spiral lamina can be seen. (see Eshraghi et al. Table-1, this issue)

Fig 6

Videofluoroscopic evaluation of two stages of an electrode insertion. These images represent two pictures taken during the videofuoroscopy evaluation of the insertion characteristics of a Nucleus contour electrode array. Before (a) and after (b) removal of the insertion stylet, the electrode is positioned at a more perimodialar position (compare a with b).

Fig 7

A three-channel light delivery system with side-firing optical fibers was inserted into the cochlea via a cochleostomy created near the round window niche. The light delivery system was stabilized with dental acrylic. A) Shows a micro-Computed Tomography reconstructed section of a cat cochlea with the placed three-channel light delivery system (optical fibers). B) This is a sketch of panel A. (Courtesy: Drs. Claus-Peter Richter and Suhrud M. Rajguru).Structures that can be identified are labeled: SV=scala vestibuli, N=auditory nerve, SG=spiral ganglion, bone=otic capsule bone.