Skip to content

Overview

Theo Murphy meeting organised by Dr Bob Carlyon and Dr Deborah Vickers

Cochlear implants (CIs) restore hearing to deaf people by electrically stimulating the auditory nerve (AN). This meeting will focus on the limitations and successes of CIs and on new methods for improving them. Topics include new methods of stimulating the AN, measuring AN survival so as to aid patient-specific processing, understanding the brain changes that occur when hearing is restored by a CI, and how to best combine CI stimulation with residual acoustic hearing. 

Poster Session

There will be a poster session at the meeting venue.

Attending this event

This meeting is intended for researchers in relevant fields and will take place at Eastwood Hall, Mansfield Road, Eastwood, Nottingham NG16 3SS.

  • Free to attend (registration essential)
  • Accommodation and catering to be paid for by participants
  • Limited places, advance registration essential

Enquiries: contact the Scientific Programmes team

Organisers

Schedule


Chair

Dr Karolina Kluk

Manchester Centre for Audiology and Deafness (ManCAD) and The University of Manchester, UK

09:05-09:35
Drug delivery for improved cochlear implant performance

Abstract

Abstract will be available soon
09:35-09:50
Discussion
09:50-10:20
Towards the optical cochlear implant: optogenetic stimulation of the auditory pathway

Abstract

As light can be spatially confined, optogenetic cochlear implants (oCI) promise to overcome the limited spectral resolution of the current electrical cochlear implant (eCI). Proof of principles studies have demonstrated the feasibility of an optogenetic approach to restore hearing in deaf animals. Towards its development to a clinical application, multiple tasks spanning from the optimising oCI stimulation of the spiral ganglion neurons (SGN) to demonstrating, using oCI prototypes, enhanced frequency resolution have to be tackled. The presentation will emphasise optogenetic stimulation of the SGNs which requires the expression of the most suitable light-sensitive protein (channelrhodopsin) and identify the optimal stimulation parameters in order to define the sound coding strategies of the future oCI. 

Speakers

10:20-10:35
Discussion
10:35-11:05
Break
11:05-11:35
Enhanced transmission of temporal fine structure with a penetrating auditory-nerve electrode

Abstract

Most cochlear-implant users show only limited sensitivity to temporal fine structure (TFS), which results in impaired pitch discrimination and impaired sound recognition amid competing sounds. In a feline animal model, a penetrating auditory-nerve electrode can selectively stimulate fibers from the cochlear apex. Such apical stimulation permits transmission of TFS at higher rates than is obtained by stimulation of the more-basal cochlear regions that are accessed by today’s cochlear implants. Ongoing psychophysical experiments in cats, coupled with non-invasive scalp-recorded electrophysiological measures, are testing whether the enhanced TFS transmission that has been demonstrated with invasive physiological methods is evident as improved temporal pitch perception. Normal-hearing cats could detect changes in the rates of high-frequency band-passed pulse trains, demonstrating non-spectral temporal pitch perception. In those animals, the scalp-recorded Acoustic Change Complex (ACC) showed a similar sensitivity to pulse-rate changes, suggesting that ACC can be used as a surrogate for psychophysical measures. A scalp-recorded Frequency Following Response (FFR) was evident across the relevant range of pulse rates. Electrical cochlear stimulation with either a cochlear implant or with a penetrating auditory-nerve electrode elicits robust FFR and ACC. Early results from these non-invasive measures suggest enhanced transmission of TFS by the penetrating electrode. 

Speakers

11:35-11:50
Discussion
11:50-12:15
Objective measures of sensitivity and selectivity to cochlear implant stimulation

Abstract

I will summarise some new objective measures of the sensitivity and selectivity to CI stimulation that can be applied in situations where psychophysical measures are hard to obtain, including programming CIs of young children and in animal experiments. I will focus on the “ALFIES” method, which provides a fast objective measure of sensitivity and of both spatial and temporal selectivity, using stimuli similar to those used clinically. It does so by interleaving two high-rate pulse trains, amplitude-modulated at F1 and F2 Hz respectively, corresponding to the 2nd and 3rd harmonics of a 40-Hz F0, and records a neural distortion response (NDR) with a frequency of F0 Hz using scalp electrodes. Unlike the electrical artefact the NDR has a group delay of 40 ms and does not depend on the distance between the recording electrode and the CI. It has a steep amplitude-growth function, making it suitable for programming CIs by objectively estimating most-comfortable levels. Its amplitude depends on the separation between the electrodes to which the F1 and F2 pulses are applied, thereby measuring spatial selectivity, while its dependence on the gap between the F1 and F2 pulses provides an estimate of temporal interactions in the patient’s auditory system. 

Speakers

12:15-12:30
Discussion

Chair

13:30-14:00
Electrocochleography predictions derived from a combined model of acoustic hearing and electric current spread in the cochlea

Abstract

Intracochlear electrocochleography (ECochG) is a potential tool for the assessment of residual hearing in cochlear implant users during implantation and of acoustical tuning post-operatively. It is, however, unclear how these intracochlear ECochG recordings depend on stimulus characteristics, morphology and hair cell degeneration. By combining a peripheral model of hair cell activation with a 3D volume-conduction model of the current spread in the cochlea a model was developed that can simulate intracochlear ECochG recordings. 

The goal of the study was to compare the model outcomes with real ECochG data from CI-subjects and to predict how various patterns of hair cell degeneration will influence the results. 3D volume conduction simulations showed that the intracochlear ECochG is a local measure of activation. Increasing stimulus level resulted in broader tuning. Onset responses and higher harmonics were dependent on the pattern of hair cell loss. Simulations showed that the phase responses can be reliably recorded when spatial sampling is high, but aliasing might occur when spatial under-sampling occurs. 

As the model replicated characteristics seen in intracochlear ECochG recordings in the temporal, spectral and spatial domain, it may aid in the interpretation of intra- and postoperative ECochG recordings and become a valuable tool for understanding and diagnosing the etiology of hearing loss in CI-recipients.

Speakers

14:00-14:15
Discussion
14:15-14:45
Combining stem cells and electrode arrays: Cochlear implants meets regenerative biology

Abstract

The performance of a cochlear implant relies on the auditory nerve working adequately in order to convey the information to the brain. Thus, for those with auditory neuropathies or cochlear nerve deficiencies, a cochlear implant may not be an effective therapeutic option. 

We have previously shown that we can functionally restore the cochlear nerve in a gerbil model of auditory neuropathy using stem cells. Human embryonic stem cells can be driven to produce otic neuroprogenitors (hONPs) that, in turn, can differentiate into spiral ganglion neurons. hONPs were transplanted into the cochleae of ouabain-treated gerbils, showing engraftment and functional integration. More recently, we have developed a new gerbil model with a two-pronged sensorineural hearing loss - auditory neuropathy is induced with topical ouabain and subsequently the hair cells are lesioned with a kanamycin/furosemide treatment. To model cochlear implantation, we are using a fully-implantable rodent stimulator in which the electrode is activated by a magnetic field.  

In my talk, I will present the progress achieved by combining the cochlear implant prototypes with the rebuilding of the auditory nerve using hONPs. Achieving functional integration of transplanted cells generated in vitro with a cochlear implant should expand the indication for the device, increasing the patient base that could benefit from it. 

Speakers

Professor Marcelo N Rivolta

Centre for Stem Cell Biology, University of Sheffield, UK

14:45-15:00
Discussion
15:00-15:30
Break
15:30-16:00
How plastic are auditory frequency-to-place maps?

Abstract

To what extent is the human auditory system plastic? More specifically, can listeners adapt to a mismatch between the frequency-place map determined by physiology and that imposed by a cochlear implant? CI users with single-sided deafness (SSD) present a very interesting platform to investigate this issue because they have access to the normal physiological frequency-place function in their normal hearing ear, and to the cochlear implant frequency-place function in the other ear. In this study SSD CI users manipulated the output frequency range of a channel vocoder to make it sound as similar as possible (when presented to the normal hearing ear) to the percepts obtained through the cochlear implant. The vocoders’ analysis filters were fixed and identical to those in the cochlear implant. A wide range of different vocoders were selected by individual SSD-CI users. The amount of frequency mismatch implicit in those selections was clearly influenced by electrode location and by experience with the CI, with deeper insertions and longer experience being associated with less mismatch. Taken together, these results suggest that adult listeners are able to adjust to frequency mismatch to some extent, but not all listeners adapt completely. This result has significant implications for understanding speech perception outcomes in adult CI users.

Speakers

16:00-16:15
Discussion
16:15-16:45
Relevance of temporal cue processing on speech perception for cochlear implant users

Abstract

Speech information transmission in cochlear implant (CI) users is reliant upon the ability to detect, track, discriminate and process the amplitude-modulated (AM) envelope of speech sounds independently in different channels.  Information transmission through the electrically stimulated auditory pathway can be hindered at many stages due to, for example, spread of electrical current, survival of inner-ear neurons and the neural representation of dynamic spectro-temporal cues.  In this research we objectively (electroencephalogy (EEG), 64-channel Biosemi) measured the cortical representation of AM stimuli (15 versus 40Hz) using the alternating auditory change complex (ACC) paradigm to understand neural processing of dynamically changing AMs. We used a slow (0.5Hz) alternating rate between different AM frequencies, to evoke a transient cortical ACC, and a faster alternating rate to trigger neural adaptation (6-7Hz) to elicit the auditory change following response (AC-FR).   Adult normal hearing listeners (aged 18-70) and CI listeners (aged 62-80) were tested. We found that CI and normal hearing listeners are sensitive to changes in AM frequency but CI listeners were poorer at tracking higher alternation rates.  We attribute this to greater cortical adaptation.  This has implications for parsing syllables in running speech, grouping perceptual objects, affecting listening strategies, listening effort and every day communication.  

Speakers

16:45-17:00
Discussion

Chair

09:00-09:30
Neural strategies for adapting to changing auditory inputs

Abstract

A capacity to adapt to altered inputs is critical for maintaining perceptual abilities following sensory impairments. We have shown that the auditory system can compensate for changes in the balance of inputs between the two ears, both during development and in later life, and maintain accurate sound localization in spite of reduced hearing in one ear. Our research in animals and humans has demonstrated that this can be achieved either through adaptive shifts in neuronal sensitivity to the altered binaural cues or by reweighting different spatial cues according to their relative reliability. The degree to which each strategy for adaptation is used depends on the way that subjects are trained, suggesting that targeted training strategies may be helpful for restoring sound localization in clinical populations according to their residual hearing ability and therefore the localization cues that remain available. Importantly, our recent work suggests that adaptation to asymmetric hearing loss generalizes to untrained sounds and to more challenging listening conditions. Furthermore, we have shown that visual information can influence auditory spatial judgments and the weighting of different spatial cues, and that a multisensory training paradigm can help to improve auditory spatial processing and perception following bilateral cochlear implantation. 

Speakers

09:30-09:45
Discussion
09:45-10:15
Deficient recurrent processing and top-down interactions in the congenitally deaf brain

Abstract

Abstract will be available soon

Speakers

10:15-10:30
Discussion
10:30-11:00
Break
11:00-11:30
Homo Cyberneticus: Neurocognitive embodiment of artificial limbs

Abstract

To successfully design devices for the human body, engineers often view the body itself as the ideal design template. Similarly, for individuals missing a limb, the development of artificial prosthetic limbs often centers on embodiment as the goal: focusing device design and control on becoming more like our biological bodies. But ultimately, the success of artificial limb will critically depend on its neural representation in our brains. Importantly, neurocognitive resources might differ radically, depending on the user’s life experiences and needs. Here I will present a series of studies where we investigated the neural basis of artificial limb use for both substitution and augmentation technologies. We find that contrary to folk wisdom, the brain does not assimilate neural representations for the artificial limb with those for the biological body, creating opportunities for novel technological interfaces. Collectively, these studies suggest that although, in principle, opportunities exist for harnessing hand neural and cognitive resources to control artificial limbs, alternative non-biomimetic approaches could be also well suited for successful human-device interface.  

Speakers

11:30-11:45
Discussion
11:45-12:15
Neural coding and plasticity with cochlear implants

Abstract

Cochlear implant (CI) users with a prelingual onset of hearing loss show poor sensitivity to interaural time differences (ITDs), an important cue for sound localization and speech reception in noise. Similarly, neural ITD sensitivity in the inferior colliculus (IC) of neonatally-deafened animals is degraded compared with animals deafened as adults. Here, neonatally-deafened rabbits were provided with chronic bilateral CI stimulation to investigate whether auditory experience through bilateral CIs during development can reverse the effect of early-onset deafness on ITD sensitivity. In the early-deaf rabbits that received chronic stimulation during development, the prevalence of ITD sensitive neurons was restored to the level of adult-deaf rabbits. Also neural ITD sensitivity in the early-deaf and stimulated rabbits improved partially. In contrast, chronic CI stimulation did not improve temporal coding in early-deaf rabbits. These findings highlight the importance of auditory experience during development on the maturation of binaural circuitry.

Speakers

12:15-12:30
Discussion
12:30-13:15
Lunch
13:15-13:45
Impact of auditory deprivation and plasticity on binaural hearing in CI users

Abstract

Our lab studies children and adults who receive bilateral cochlear implants (BiCI), or adults with single-sided deafness receiving a CI in the deaf ear (SSD-CI). Bilateral hearing typically improves localization of sounds and segregation of speech from background noise compared with unilateral hearing. However, patients typically perform worse than normal hearing listeners. We use several approaches to understand mechanisms driving gaps in performance, including asymmetry in sensitivity to monaural information such as modulation detection. Further interaural mismatch in place of stimulation along the cochlea, age at onset of deafness and age at implantation contribute to recovery of binaural hearing. Because CI processors do not preserve binaural cues with fidelity, we use research processors to generate multi-channel binaural stimulation strategies that introduce different rates of stimulation across the electrode arrays, thereby preserving rates that are important for both binaural sensitivity and speech understanding. In addition, eye gaze studies reveal developmental factors that in decision-making that are not observed with measures of threshold. Finally, pupillometry studies provide insight into the impact of integrating inputs from two ears, whereby in some instances improved performance with two ears can be “costly” in the listening effort domain.

Speakers

13:45-14:00
Discussion
14:00-14:30
Simulation of spatial hearing of bilateral CI users with an electrically stimulated excitatory-inhibitory (EI) interaction model

Abstract

Bilateral cochlear implants (CIs) greatly improve the spatial hearing of CI users compare to those with only one implant. However substantial gaps still exist between bilateral CI users and normal hearing listeners in different aspects, such as their lateralization and localization performance. Computer models are expected to partially reveal the possible reasons behind such gaps, by dissecting the specific contribution of each stage along the whole processing chain. In order to provide a model framework for predicating bilateral CI users’ lateralization or localization performance in a variety of experimental scenarios, here a recently published electrically stimulated single excitation-inhibition (EI) model neuron (Hu et al. 2022, JARO) was extend to population-EI-model neurons. The proposed model framework includes (a) parameter initialization, (b) binaural signal generating, (c) switchable CI processing, (d) auditory nerve (AN)- and EI- neuron processing, and (e) decision model stages. For demonstration purposes, several bilateral CIs experiments were simulated, such as pulse rate limitation of ITD sensitivity; left/right discrimination or lateralization; free-field localization with and without two independent automatic gain controls (AGCs). In general, the model framework could capture the average performance of all selected experiments even with the same EI-model units and a very simplified decision model.

Speakers

14:30-14:45
Discussion
14:45-15:00
Break
15:00-15:30
Can two cochlear implants promote development of one binaural hearing system in children?

Abstract

Bilateral cochlear implants (CIs) have provided hearing advantages over use of a single CI in children with deafness in both ears. Yet, the goal of promoting normal binaural/spatial hearing development in these children remains elusive.  Evidence of remaining abnormalities in children using bilateral CIs comes from behavioral measures of impaired sound localization and sensitivity to binaural cues. These challenges may reflect abnormalities in integration of bilateral CI input in the auditory brainstem and cortex, including disruptions in functional connectivity, as measured with electrophysiology in children. We suggest that mismatches in bilateral CI input contribute to binaural/spatial hearing challenges by creating an aural preference for one ear when implantation of the opposite ear is delayed or allowing ongoing asymmetries or mismatches in stimulation of the two ears. While the former problem can be addressed through early access to CI in each candidate ear, there is no present protocol to harmonize the separate program parameters and processing of independent CIs.  Present studies seek to identify these sources of mismatched bilateral CI input and to provide methods that might be used to resolve these challenges to binaural hearing development.

Speakers

15:00-15:30
Discussion
15:45-16:15
Neural plasticity constrains the sound of a cochlear implant

Abstract

Abstract will be available soon
16:15-16:30
Discussion
16:30-17:00
Panel discussion

Speakers