Characterization and Modeling of the Electrode-nerve Interface for Electric-acoustic Stimulation in Cochlear Implant Users PDF Download

Author: Daniel Kipping
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Author: Johannes Benjamin Krüger
Publisher:
ISBN: 9783843953627
Category :
Languages : en
Pages : 0

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Author: Tania Hanekom
Publisher:
ISBN:
Category :
Languages : en
Pages :

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The objective of this thesis is to provide additional insight into the electrode array-nerve fibre interface that exists in the implanted cochlea and to facilitate investigation of new electrode arrays in interaction with the cochlea and auditory nerve fibres. The focus is on potential distributions and excitation profiles generated by different electrode array types and factors that could have an influence on these distributions and profiles. Research contributions made by the thesis are the creation of a detailed 3-D model of the implanted cochlea that accurately predicts measurable effects in cochlear implant wearers and facilitates effortless simulation of existing and new electrode array variations: the establishment of the important anatomical structures required in a 3-D representation of the implanted cochlea: establishment of evidence that array location is the primary parameter that controls spread of excitation: definition of the critical focussing intensity of intracochlear electrode pairs: confirmation thatmonopolar stimulation could deliver focussed stimulation to approximately the same degree than that delivered by widely spaced electrode configurations and that the use of monopolar configurations over bipolar configurations are therefore advantageous under certain conditions: explanation of the effect that encapsulation tissue around cochlear implant electrodes could have on neural excitation profiles: extension of the information available on the focussing ability of multipolar intracochlear electrode configurations: and establishment of evidence that a higher lateral electrode density could facilitate better focussing of excitation, continuous shaping of excitation profiles and postoperative customization of electrode arrays for individual implant wearers.

Author: Frank Rattay
Publisher: Springer Science & Business Media
ISBN: 3709132711
Category : Technology & Engineering
Languages : en
Pages : 266

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Functional electrical stimulation is the most important application in the field of clinical treatment with currents or magnetism. This technique artificially generates neural activity in order to overcome lost functions of the paralized, incontinent or sensory handicapped patient. Electricity and magnetism is also used in many cases, e.g., to stimulate bone growth or wound healing. Nevertheless, the basic mechanism of the artificial excitation of nerve and muscle fibers has become known only in the last few years. Although many textbooks are concerned with the natural excitation process there is a lack of information on the influence of an applied electrical or magnetic field. This book, written for students and biomedical engineers, should close the gap and, furthermore, it should stimulate the design of new instrumentation using optimal strategies.

Author: Aayesha Narayan Dhuldhoya
Publisher:
ISBN:
Category : Acoustic nerve
Languages : en
Pages : 202

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Masker pulse trains that are lower in level than the probe pulse produced proportionally small decrements in the ECAP amplitude with complete recovery within 250 ms of pulse train offset particularly in adults. ECAP recovery of a probe preceded by a masker pulse train of equal level followed a monotonic or non-monotonic pattern consistent with a hypothesis of both adaptation and facilitation occurring with pulse train stimulation. The various patterns of recovery may attest to the occurrence of more than a single process in the same subset of nerve fibers or in different fibers. We hypothesize that the variations in the recovery patterns may be attributable to individual differences in the status of the auditory nerve and possibly, the variations in temporal interactions across the spatial domain at different stimulus levels. Finally, the probe-evoked ECAP amplitude at steady state in children and briefly, e.g., 20 ms, after pulse train offset in both age groups could be predicted by the ECAP amplitude in response to the same probe pulse when preceded at a brief interval (1.2 or 2 ms) by a single masker pulse of the same level as the masker pulse train. Further investigation may reveal if the observed differences in neural responsiveness to pulsatile stimulation, among individuals account for differences in psychophysical measures, including speech perception and whether there may be an "optimal" neural output that could be evoked by an individually "optimized" signal.

Author: Hussnain Ali
Publisher:
ISBN:
Category : Cochlear implants
Languages : en
Pages : 478

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The peripheral sensory auditory system is an intricate synergy between mechanical, chemical, and electrical bio-systems that generate complex temporal-spectral patterns of neural activity for sound perception. Artificial electrical stimulation provided by contemporary multichannel cochlear implants (CIs) aim to mimic the natural electrical stimulation patterns that occur at the spiral ganglion nerves; however, sparsity of information provided by the CIs is beyond comparison to the exquisite intricacies of a normal auditory system. This, in part is due to the current limitations inherent in the design of CIs, particularly the electrode-nerve interface, which may be a bottleneck for optimal performance. Spectral mismatch, poor temporal and spectral resolution, and current spread combined with patient-specific physiological, audiological, and cognitive factors are some of the key challenges that may impact performance and could potentially be responsible for large variations in CI performance outcomes. Although electrode placements relative to the spiral ganglion are generally unknown, conventional sound coding algorithms and clinical fitting procedures follow a one-size-fits-all strategy. This dissertation aims to customize/personalize the sound coding and fitting procedures according to an individual’s cochlear physiology. This is achieved by utilizing novel imaging procedures, more specifically CT images of recipients’ cochleae, to determine the precise spatial location and orientation of the electrode contacts and the corresponding neural stimulation sites to produce a tailor-fit frequency-to-place function. In addition, patient-specific channel selection optimization techniques have been presented that aim to optimize presentation of electrical stimulation patterns. The proposed schemes have been evaluated in groups of normal hearing individuals using CI simulations as well as cochlear implant recipients. The data from the experiments suggest that patient-specific sound coding and fitting schemes may potentially aid in achieving higher asymptotic performance and possibly faster adaptation to electric hearing.

Author: Covey Ashe Denton
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 296

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Author: Thomas Lenarz
Publisher:
ISBN: 9783805591478
Category : Cochlear implants
Languages : en
Pages : 0

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This issue is a dedicated supplement published in addition to the regular issues of 'Audiology and Neurotology' focussing on one specific topic. 'Audiology and Neurotology' is a well-respected, international peer-reviewed journal in Otorhinolaryngology. Supplement issues are included in the subscription.

Author: Daniel Alrutz
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Matthew Charles Schoenecker
Publisher:
ISBN:
Category :
Languages : en
Pages : 186

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Cochlear implants (CIs) are neural prostheses that currently provide acoustic sensation to more than 120,000 profoundly hearing-impaired people throughout the world. The majority of these CI users are able to understand speech without lip reading and to converse over the telephone. The most fortunate among them can even perform and appreciate music. Unfortunately, however, many CI recipients receive much less benefit from their devices. In order to examine the neuronal bases for these disparate outcomes, a recording system was developed to overcome specific technical limitations in previous studies that recorded neuronal responses to cochlear implant stimulation in animal models. This recording system was then used in two studies comparing responses to normal acoustic stimulation and electrical cochlear implant stimulation in guinea pigs and cats. The design of the recording system included a 32-channel recording amplifier and a software technique for removing stimulus artifacts from recordings of neural responses to high-rate electrical stimulation. Contemporary cochlear implants often deliver current pulse trains with carrier rates of 1000 pulses/s or higher. In neurophysiology studies, this electrical stimulation produces artifacts that are typically much larger than neuronal responses. Therefore, the recording system was specifically designed to record neuronal responses and cancel these electrical stimulus artifacts. When biphasic full-scale-input pulses (1.5-V) are applied directly to the amplifier inputs, each recording channel settles to 20 micro-volts in less than 80 microseconds. This fast recovery makes it likely that the recording electrode-electrolyte interface, not the recording electronics, will limit artifact settling times. Artifacts are blanked in software, allowing flexibility in the choice of blanking period and the possibility of recovering neural data occurring simultaneously with non-saturating artifacts. The system has been used in-vivo to record central neuronal responses to intracochlear electrical stimulation at rates up to 2000 pulses/s. Using this recording system, systematic and quantitative comparisons of inferior-colliculus responses to acoustic stimulation and electrical stimulation in two configurations (monopolar and bipolar) were carried in guinea pigs and cats. Previous cochlear implant studies using isolated electrical stimulus pulses in animal models have reported that monopolar stimulus configurations elicit broad extents of neuronal activation within the central auditory system--much broader than the activation patterns produced by bipolar electrode pairs or acoustic tones. However, psychophysical and speech reception studies that use sustained pulse trains do not show clear performance differences between monopolar and bipolar configurations. To evaluate whether monopolar intracochlear stimulation can produce selective excitation of the inferior colliculus, activation widths were determined along the tonotopic axis of the inferior colliculus for acoustic tones and 1000-pulse/s electrical pulse trains in guinea pigs and cats. Electrical pulse trains were presented using an array of 6-12 stimulating electrodes distributed longitudinally along a space-filling silicone carrier positioned in the scala tympani of the cochlea. The data indicated that for monopolar, bipolar, and acoustic stimuli, activation widths were significantly narrower for sustained responses than for the transient response to the stimulus onset. Furthermore, monopolar and bipolar stimuli elicited similar activation widths when compared at stimulus levels that produced similar peak spike rates. Surprisingly, monopolar and bipolar stimuli produced narrower sustained activation than 60 dB SPL acoustic tones when compared at stimulus levels that produced similar peak spike rates. Therefore, the conclusion from these experiments was that intracochlear electrical stimulation using monopolar pulse trains can produce activation patterns that are at least as selective as bipolar or acoustic stimulation, if stimulus intensities are appropriately matched. The second study compared responses to acoustic and monopolar electrical stimuli that were sinusoidally amplitude modulated (SAM), in order to better model the complex signals delivered by CI processors. For both normal hearing listeners and cochlear implant users, SAM signals produce psychophysical interactions that can extend across large differences in carrier frequency or large intracochlear electrode separations. However, the neural correlates of these phenomena are not well understood. This study was designed to determine whether SAM stimuli elicit activation across a broader extent of the frequency axis of the inferior colliculus than unmodulated steady-state stimuli, and whether this activation is strongly phase locked to the SAM stimulus envelope. To address these questions neuronal activity in the inferior colliculus of guinea pigs, normal cats and chronically deafened cats was recorded in response to acoustic and electrical stimulation. Quantitative analysis of recordings indicated that the extent of inferior colliculus activation was up to 70% broader for SAM stimuli than for unmodulated steady-state stimuli in normal cats and guinea pigs and 160% broader in chronically deafened cats. This activity was also phase-locked to the SAM envelope across a broad extent of the frequency axis of the inferior colliculus. These results suggest that a number of cross-carrier frequency interactions for SAM stimuli could occur at the level of the inferior colliculus. They also show that direct comparisons of responses to acoustic and electrical SAM stimuli can reveal attributes of neural processing that underlie specific psychophysical findings in CI recipients--and thereby can provide a powerful basis for guiding development of new processing strategies for future cochlear implants.