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A Tribute to a Remarkably Sound Solution

2013; Cell Press; Volume: 154; Issue: 6 Linguagem: Inglês

10.1016/j.cell.2013.08.047

1097-4172

Peter S. Roland, Emily A. Tobey,

Neuroscience and Music Perception

For their work on the development of the modern cochlear implant, which bestows hearing to individuals with profound deafness, Ingeborg Hochmair, Graeme Clark, and Blake Wilson are the 2013 recipients of the Lasker∼DeBakey Clinical Medical Research Award. For their work on the development of the modern cochlear implant, which bestows hearing to individuals with profound deafness, Ingeborg Hochmair, Graeme Clark, and Blake Wilson are the 2013 recipients of the Lasker∼DeBakey Clinical Medical Research Award. Ingeborg Hochmair, Graeme Clark, and Blake Wilson each lead a team of professionals dedicated to aiding the many individuals with hearing impairment. The Lasker Foundation now recognizes their scientific contributions to the development of cochlear implants, and in so doing acknowledges the effort of many individuals, both past and present, in the field of cochlear implantation, widely recognized as one of the most successful achievements in modern medicine. Cochlear implants now routinely make it possible for young congenitally deaf children to communicate orally and restores aspects of hearing for many adults who lose their hearing later in life. Cochlear implants represent the first technology to successfully replace and augment a biologic sense organ (Loizou, 1999Loizou P.C. IEEE Eng. Med. Biol. Mag. 1999; 18: 32-42Crossref PubMed Scopus (142) Google Scholar). The device consists of internal and external hardware that use a microphone to collect acoustic signals, process the signal using sophisticated software to decompose, and translate the signal into electrical pulses that can be transmitted to a surgically implanted electrode array placed in the cochlea. These signals stimulate the auditory nerve, and the brain learns to interpret the signals as speech or other sounds. Cochlear implants assist many individuals who are totally deaf or very nearly totally deaf to engage in conversational speech without using visual cues. A high percentage of cochlear implant recipients converse by speaking and listening, including talking on the telephone, with little difficulty. To date, over 300,000 severely or profoundly hearing impaired individuals have received cochlear implants worldwide. For many of these individuals, cochlear implants provide a substantial increase in their quality of life by opening up a large universe of employment and recreational opportunities. Consequently, the cost-benefit ratio for cochlear implantation is extremely high, exceeding by a large margin the cost benefit of many commonly performed medical procedures, including total hip replacements (Wyatt et al., 1996Wyatt J.R. Niparko J.K. Rothman M. deLissovoy G. Laryngoscope. 1996; 106: 816-821Crossref PubMed Scopus (86) Google Scholar). Recently, several review articles have been published exploring and documenting the historical road traveled to develop cochlear implants (Clark, 2008Clark G.M. J. Rehabil. Res. Dev. 2008; 45: 651-693Crossref PubMed Scopus (34) Google Scholar, Wilson et al., 2011Wilson B.S. Dorman M.F. Woldorff M.G. Tucci D.L. Prog. Brain Res. 2011; 194: 117-129Crossref PubMed Scopus (30) Google Scholar). Common themes among these historical reviews include recognizing the contributions made in the late 1700s by individuals who invented electricity via a capacitor system, the Leyden jar, or via early batteries. Early publications from individuals, such as Volta, provide important glimpses into man's initial fascination with electricity and its possible interaction with the body. Accounts of the social impact of deafness on individuals during these early periods often reflect back to the poignant words and experiences of Ludwig van Beethoven and Helen Keller who experienced significant hearing losses. Beethoven, in letters to his brothers, wrote, "For me there can be no relaxation in human society; no refined conversations, no mutual confidences. I must live quite alone and may creep into society only as often as sheer necessity demands.…Such experiences almost made me despair and I was on the point of putting an end to my life—the only thing that held me back was my art… [And] thus I have dragged on this miserable existence" (Lockwood, 2003Lockwood L. Beethoven: The Music and the Life. W. W. Norton and Company, New York, N. Y.2003Google Scholar). Helen Keller stated, "I am just as deaf as I am blind. The problems of deafness are deeper and more complex, if not more important, than those of blindness. Deafness is a much worse misfortune. For it means the loss of the most vital stimulus—the sound of the voice that brings language, sets thoughts astir and keeps us in the intellectual company of man" (Keller, 1933Keller H. Helen Keller in Scotland. Methuem and Company, London1933Google Scholar). Djourno and Eyries, 1957Djourno A. Eyries C. Presse Med. 1957; 65: 1417PubMed Google Scholar were the first to report that electrical current passed through the auditory nerve produced an auditory sensation. During the early 1960s, several investigators, including William House and Blair Simmons, led teams investigating electrical stimulation of the auditory nerve (Mudry and Mills, 2013Mudry A. Mills M. JAMA Otolaryngol. Head Neck Surg. 2013; 139: 446-453Crossref PubMed Scopus (80) Google Scholar). Subjects not only experienced an auditory percept but showed some ability to distinguish differences in sounds of different frequencies. House placed a single ball electrode inside the cochlea to stimulate the auditory nerve. The majority of individuals receiving this single-channel cochlear implant perceived environmental sounds and distinguished differences between many of them. Complex spectral discrimination, however, remained poor by current day standards, and few individuals recognized words or understood complex spoken language. House was, however, able to demonstrate that auditory percepts generated by electrical signals from the implanted device significantly enhanced lip reading and, thereby, enhanced the ability to communicate. House's early efforts were met with great skepticism; he performed his work with little encouragement and in the face of some hostility. While most early proponents believed cochlear implants would restore some useful hearing for adult recipients who lost their hearing after they acquired language, most proponents believed that implants would have limited to no role in the management of children with congenital deafness. Yet, one of the most important achievements of current cochlear implant technology is the ability to restore aspects of hearing to many congenitally deaf children who consequently, learn spoken language. Emminent auditory physiologists including, Merle Lawrence, declared electrical stimulation of the cochlear nerve would never permit speech understanding. Cochlear implants achieved scientific "legitimacy" in 1975 when the National Institute of Health sponsored the research studies undertaken by Bilger and his colleagues. The resulting "Bilger Report" confirmed some speech perception benefit of cochlear implantation in 13 subjects. The history of the development of cochlear implants can be divided into four steps: (1) proof of concept—it had to be shown that electrical stimulation of the auditory nerve in hearing impaired persons produced a useful auditory percept; (2) development of devices that could be safely implanted by a variety of surgeons with minimal risk and which could be tolerated by recipients for many years without damaging the auditory system or surrounding structures; (3) development of devices that used the tonotopic organization of the cochlea to allow the recipient to discriminate between pitches; (4) development of algorithms that converted auditory signals into pulse trains to stimulate multiple sites and maximize speech recognition. Many of the principal contributors to step 1, including Djourno, Eyriés, House, and Simmons, are now deceased. Critical contributions for step 2 were made by the Hochmair team. The Hochmair and Clark teams working separately achieved step 3, and Wilson and his team developed the speech coding strategies critical for step 4. Hochmair's leadership initially focused on developing reliable cochlear implant systems that used a single site of stimulation either within or just outside the cochlea. These devices were well tolerated and allowed limited speech recognition. The Med-El Corporation (Innsbruck, Austria), now the second largest commercial provider of cochlear implants, was founded by Hochmair and developed the first system providing a behind-the-ear processor and associated transmitting coil. Her team is known for rigorous physical studies and Med-El Corporation has supported fundamental and clinical research at leading universities throughout the world. The behind-the-ear processor made cochlear implants desirable to a variety of recipients and is used by many devices today. Hochmair also was pivotal for step 3. Her team developed active electrodes in an implanted stimulator/receiver and an array of electrodes imbedded in a silicone carrier. As shown in Figure 1, electrode design and placement are critical for successful cochlear implantation. These two fundamental design features are still used by currently marketed devices. A system with these features was first implanted in Vienna on December 16, 1977. A similar system was implanted by Clarke's team in Melbourne in August of 1978. Clarke and his team of scientists and clinicians investigated many aspects of cochlear implantation, including physiology, biology, pathology, bioengineering, psychophysics, and speech processing. In addition, his investigators have explored how the devices influence communication development. Clark's teams have produced the highest number of publications from a single institution in cochlear implantation across the world and made many important scientific discoveries advancing the field. His teams have also explored applying knowledge obtained from cochlear implants to other sensory systems, notably the tactile system, through his "Tickle Talker." Clark's devices are marketed by Cochlear Corporation (Sydney, Australia) which continues to support research around the world, including in Australia, to further develop the implant devices. Wilson spent the majority of his career working at the Research Triangle Park in North Carolina and received his principle funding through a continuous series of National Institutes of Health grants and contracts. In 1991, Wilson developed a new method of encoding acoustic information into electrical impulses, which permitted much improved speech recognition. This speech coding strategy was termed continuous interleaved sampling (CIS). This development was reported in Nature in 1991 and remains the most highly cited publication in the field of cochlear implants (Wilson et al., 1991Wilson B.S. Finley C.C. Lawson D.T. Wolford R.D. Eddington D.K. Rabinowitz W.M. Nature. 1991; 352: 236-238Crossref PubMed Scopus (909) Google Scholar). CIS is still used as a processing option in all the cochlear implant systems manufactured by the "big three" cochlear implant companies, which reach more than 99% of the global market. Other speech coding strategies are available, but the majority are either the same or refinements of those described by Wilson and his team over the years. All the intellectual property developed by Wilson and his team has been donated to the public domain. As one would expect, a large number of individuals made contributions in the development of cochlear implants. In this paragraph, we will mention only a few of the others. Donald Eddington, for example, working at the University of Utah, made critical advances in the development of implants that stimulated multiple sites. Eddington's work was critical in the design of the Symbion and Ineraid cochlear implants, which, at one point, had individuals with the highest speech recognition scores. Because the Ineraid had a transcutaneous port that permitted access to and manipulation of the internal components, Ineraid patients were highly sought as research subjects long after manufacture of the device was discontinued. Michael Merzenich also made important contributions in the area of neuroplasticity. Working together with Robin Michelson and Robert Schindler at the University of California, Merzenich completed important work developing the Advanced Bionics device. Advanced Bionics Corporation (Valencia, CA) has now become the third largest manufacturer of cochlear implants. As indicated by the Lasker Foundation Award, cochlear implants represent a technology that brings sound to many individuals who otherwise would experience diminished or absent sound in their environments. The field continues to grow and flourish as individuals around the world design more sophisticated electrodes, improve surgical techniques, develop smaller and more efficient hardware, document the communication benefits achieved by young children using the devices, explore methods of enhancing the coding of tonal languages, improve the processing of speech in noisy environments, explore whether performance is further enhanced with two versus a single cochlear implant, inquire whether the devices would provide equal or greater benefit to individuals with greater amounts of residual hearing who use conventional hearing aids, determine the optimal age to implant young children, and to explore the importance of habilitation intervention programs in further enhancing the benefits provided to communication by the devices. The entire field congratulates Ingeborg Hochmair, Graeme Clark, and Blake Wilson on their leadership and contributions to the field of cochlear implantation. The contributions made by their teams of investigators to the field of cochlear implantation are well deserving of the 2013 Lasker Foundation Award.