Morphological examination of the human temporal bone in the apical region supports the benefits of deep electrode insertion. Initiation of spikes on peripheral processes close to the basilar membrane would provide improved channel selectivity during electrical stimulation but recruiting of nerve fibres requires a higher current. A clinical study was performed on 10 users of the MED-EL COMBI 40 + implant to evaluate the effect of the insertion depth of the cochlear implant electrode on speech perception. All subjects were implanted with the standard COMBI 40 + electrode with an insertion depth of > 30 mm. Acute speech tests were carried out in which stimulation was restricted to the apical, middle and basal regions of the cochlea in turn, and using electrode arrangements in which contacts were either distributed over the whole length of the cochlea or concentrated at the basal end, thus mimicking an insertion depth of approximately 20 mm only. The results showed that stimulation of the apical region of the cochlea supports a significant degree of speech understanding, and that distributing the contacts over the whole length of the cochlea improves speech perception in quiet and in noise.
201areas, MED-EL's research focuses on providing additional pitch information. One means to achieve this could be to increase the information per time unit (information rate) delivered to the cochlea; this can be done by increasing the stimulation rate. Another way would be to add additional information into the stimulation patterns such as temporal as well as spatial fine structure information. This will be further discussed in the development of speech-coding strategies section.In addition, this article provides an overview of the new technology incorporated in the MED-EL MAESTRO CI system, reviews recent research on bilateral cochlear implantation and electric-acoustic stimulation, and describes current research efforts on developing a CI device with drug delivery capability. The MAESTRO CI SystemThe MED-EL MAESTRO CI system comprises the PULSARCI 100 and SONATATI 100 CIs, which incorporate the I 100 electronics platform; the speech processors and the MAESTRO system software, together with the Diagnostic Interface Box II, is the link C ochlear implants (CIs) are a well-known and accepted treatment method for adults and children with severe to profound hearing loss. There has been much progress in the CI field since the article detailing trends in cochlear implantation. 1 Advances in technology, increased confidence in experience, and changes in candidacy have led to CIs being made available to a larger population.Recent CI recipients perform much better than those who received implants many years ago. Back then, CI performance focused on differentiating between the presence and absence of sound or female versus male voice. Expectations for recent CI recipients, however, have changed. Their performances have been tested under increasingly difficult listening conditions. The general experiences in the CI community are that CI users usually perform very well in quiet but worse in noise, and not all CI users are able to enjoy music. For further improvements in these Cochlear implantation is an accepted treatment method for adults and children with severe to profound hearing loss. Confidence in technology has led to changes in individuals who can receive a cochlear implant and changes in expected benefit with a cochlear implant. This article describes the research and development activities at MED-EL, which make possible the implementation of new speech-coding strategies as well as the application of acoustic and electric stimulation via a combined speech processor in MED-EL devices. Research on benefits from bilateral cochlear implantation and electric-acoustic stimulation are also reviewed. Finally, the potential of drug delivery systems is considered as a way to improve cochlear implant outcomes, and results from preliminary evaluations of a hybrid cochlear implant system with drug delivery capabilities are reported. between software and speech processors or implants. The MAESTRO CI system provides fine structure information for CI users (refer to the section on speech-coding strategies). In addition, audiologi...
Present-day cochlear implants demonstrate remarkable speech understanding performance despite the use of non-optimized coding strategies concerning the transmission of tonal information. Most systems rely on place pitch information despite possibly large deviations from correct tonotopic placement of stimulation sites. Low frequency information is limited as well because of the constant pulse rate stimulation generally used and, being even more restrictive, of the limited insertion depth of the electrodes. This results in a compromised perception of music and tonal languages. Newly available flexible long straight electrodes permit deep insertion reaching the apical region with little or no insertion trauma. This article discusses the potential benefits of deep insertion which are obtained using pitch-locked temporal stimulation patterns. Besides the access to low frequency information, further advantages of deeply inserted long electrodes are the possibility to better approximate the correct tonotopic location of contacts, the coverage of a wider range of cochlear locations, and the somewhat reduced channel interaction due to the wider contact separation for a given number of channels. A newly developed set of strategies has been shown to improve speech understanding in noise and to enhance sound quality by providing a more "natural" impression, which especially becomes obvious when listening to music. The benefits of deep insertion should not, however, be compromised by structural damage during insertion. The small cross section and the high flexibility of the new electrodes can help to ensure less traumatic insertions as demonstrated by patients' hearing preservation rate. This article is part of a Special Issue entitled
ObjectiveA design comparison of current perimodiolar and lateral wall electrode arrays of the cochlear implant (CI) is provided. The focus is on functional features such as acoustic frequency coverage and tonotopic mapping, battery consumption and dynamic range. A traumacity of their insertion is also evaluated.MethodsReview of up-to-date literature.ResultsPerimodiolar electrode arrays are positioned in the basal turn of the cochlea near the modiolus. They are designed to initiate the action potential in the proximity to the neural soma located in spiral ganglion. On the other hand, lateral wall electrode arrays can be inserted deeper inside the cochlea, as they are located along the lateral wall and such insertion trajectory is less traumatic. This class of arrays targets primarily surviving neural peripheral processes. Due to their larger insertion depth, lateral wall arrays can deliver lower acoustic frequencies in manner better corresponding to cochlear tonotopicity. In fact, spiral ganglion sections containing auditory nerve fibres tuned to low acoustic frequencies are located deeper than 1 and half turn inside the cochlea. For this reason, a significant frequency mismatch might be occurring for apical electrodes in perimodiolar arrays, detrimental to speech perception. Tonal languages such as Mandarin might be therefore better treated with lateral wall arrays. On the other hand, closer proximity to target tissue results in lower psychophysical threshold levels for perimodiolar arrays. However, the maximal comfort level is also lower, paradoxically resulting in narrower dynamic range than that of lateral wall arrays. Battery consumption is comparable for both types of arrays.ConclusionsLateral wall arrays are less likely to cause trauma to cochlear structures. As the current trend in cochlear implantation is the maximal protection of residual acoustic hearing, the lateral wall arrays seem more suitable for hearing preservation CI surgeries. Future development could focus on combining the advantages of both types: perimodiolar location in the basal turn extended to lateral wall location for higher turn locations.
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