Deafness-Induced Changes in the Auditory Pathway: Implications for Cochlear Implants

Shepherd, Robert K.; Hardie, Natalie A.

doi:10.1159/000046843

Cited by 172 publications

(125 citation statements)

References 121 publications

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“…The CI user experienced many years of altered sensory input to the auditory cortex. Absence of neurotrophic support from hair cells and supporting cells to spiral ganglion neurons likely caused at least some degree of degeneration of the auditory nerve (Linthicum and Anderson 1991;Fayad and Linthicum 2006;Shepherd and Hardie 2001). Despite this, the overall waveform shape and peak latency of responses recorded from this nonprimary auditory cortex was similar to that observed in individuals with normal hearing.…”

Section: Discussionmentioning

confidence: 85%

Direct Recordings from the Auditory Cortex in a Cochlear Implant User

Nourski

Etler

Brugge

et al. 2013

JARO

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Electrical stimulation of the auditory nerve with a cochlear implant (CI) is the method of choice for treatment of severe-to-profound hearing loss. Understanding how the human auditory cortex responds to CI stimulation is important for advances in stimulation paradigms and rehabilitation strategies. In this study, auditory cortical responses to CI stimulation were recorded intracranially in a neurosurgical patient to examine directly the functional organization of the auditory cortex and compare the findings with those obtained in normal-hearing subjects. The subject was a bilateral CI user with a 20-year history of deafness and refractory epilepsy. As part of the epilepsy treatment, a subdural grid electrode was implanted over the left temporal lobe. Pure tones, click trains, sinusoidal amplitude-modulated noise, and speech were presented via the auxiliary input of the right CI speech processor. Additional experiments were conducted with bilateral CI stimulation. Auditory event-related changes in cortical activity, characterized by the averaged evoked potential and eventrelated band power, were localized to posterolateral superior temporal gyrus. Responses were stable across recording sessions and were abolished under general anesthesia. Response latency decreased and magnitude increased with increasing stimulus level. More apical intracochlear stimulation yielded the largest responses. Cortical evoked potentials were phaselocked to the temporal modulations of periodic stimuli and speech utterances. Bilateral electrical stimulation resulted in minimal artifact contamination. This study demonstrates the feasibility of intracranial electrophysiological recordings of responses to CI stimulation in a human subject, shows that cortical response properties may be similar to those obtained in normal-hearing individuals, and provides a basis for future comparisons with extracranial recordings.

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Section: Discussionmentioning

confidence: 85%

Direct Recordings from the Auditory Cortex in a Cochlear Implant User

Nourski

Etler

Brugge

et al. 2013

JARO

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“…2 is the biological component central to the auditory nerve, including the auditory pathways in the brainstem and the auditory cortices of the implant recipient. This biological component varies widely in its functional integrity and capabilities across patients (e.g., Lee et al, 2001;Shepherd and Hardie, 2001;Sharma et al, 2002;Kral et al, 2006;Shepherd et al, 2006;Fallon et al, 2008), and this variability may explain at least in part the remaining diversity in outcomes with present-day CIs. We will return to this point later in this paper.…”

Section: Components Of Implant Systemsmentioning

confidence: 99%

“…On average, patients with short durations of deafness prior to their implants fare better than patients with long durations of deafness (e.g., Gantz et al, 1993;Summerfield and Marshall, 1995;Blamey et al, 1996). This may be the result of sensory deprivation for long periods, which adversely affects connections between and among neurons in the central auditory system (Shepherd and Hardie, 2001) and may allow encroachment by other sensory inputs of cortical areas normally devoted to auditory processing (i.e., cross-modal plasticity; see Lee et al, 2001;Bavelier and Neville, 2002). Although one might think that differences in nerve survival at the periphery could explain the variability, either a negative correlation or no relationship has been found between the number of surviving ganglion cells and prior word recognition scores, for deceased implant patients who in life had agreed to donate their temporal bones for post-mortem histological studies (Blamey, 1997;Nadol et al, 2001;Khan et al, 2005;Fayad and Linthicum, 2006).…”

Section: Likely Limitations Imposed By Impairments In Auditory Pathwamentioning

confidence: 99%

Cochlear implants: A remarkable past and a brilliant future

2008

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The aims of this paper are to (i) provide a brief history of cochlear implants; (ii) present a status report on the current state of implant engineering and the levels of speech understanding enabled by that engineering; (iii) describe limitations of current signal processing strategies and (iv) suggest new directions for research. With current technology the "average" implant patient, when listening to predictable conversations in quiet, is able to communicate with relative ease. However, in an environment typical of a workplace the average patient has a great deal of difficulty. Patients who are "above average" in terms of speech understanding, can achieve 100% correct scores on the most difficult tests of speech understanding in quiet but also have significant difficulty when signals are presented in noise. The major factors in these outcomes appear to be (i) a loss of low-frequency, fine structure information possibly due to the envelope extraction algorithms common to cochlear implant signal processing; (ii) a limitation in the number of effective channels of stimulation due to overlap in electric fields from electrodes, and (iii) central processing deficits, especially for patients with poor speech understanding. Two recent developments, bilateral implants and combined electric and acoustic stimulation, have promise to remediate some of the difficulties experienced by patients in noise and to reinstate low-frequency fine structure information. If other possibilities are realized, e.g., electrodes that emit drugs to inhibit cell death following trauma and to induce the growth of neurites toward electrodes, then the future is very bright indeed.

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“…While our initial hypothesis was that the binaural circuits operate in the same way for acoustic and electric stimulation, changes in the response properties of auditory neurons resulting from deafness-induced plasticity (for review, see Shepherd and Hardie 2001;Butler and Lomber 2013) may also contribute to the degraded perceptual ITD sensitivity in bilateral CI users. For example, the model shows a strong dependence of ITD sensitivity on total synaptic strength, with higher frequency stimulation requiring a greater total synaptic conductance.…”

Section: Comparison Of Responses To Electric and Acoustic Stimulationmentioning

confidence: 99%

Modeling Binaural Responses in the Auditory Brainstem to Electric Stimulation of the Auditory Nerve

Chung

Delgutte

Colburn

2014

JARO

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Bilateral cochlear implants (CIs) provide improvements in sound localization and speech perception in noise over unilateral CIs. However, the benefits arise mainly from the perception of interaural level differences, while bilateral CI listeners' sensitivity to interaural time difference (ITD) is poorer than normal. To help understand this limitation, a set of ITD-sensitive neural models was developed to study binaural responses to electric stimulation. Our working hypothesis was that central auditory processing is normal with bilateral CIs so that the abnormality in the response to electric stimulation at the level of the auditory nerve fibers (ANFs) is the source of the limited ITD sensitivity. A descriptive model of ANF response to both acoustic and electric stimulation was implemented and used to drive a simplified biophysical model of neurons in the medial superior olive (MSO). The model's ITD sensitivity was found to depend strongly on the specific configurations of membrane and synaptic parameters for different stimulation rates. Specifically, stronger excitatory synaptic inputs and faster membrane responses were required for the model neurons to be ITD-sensitive at high stimulation rates, whereas weaker excitatory synaptic input and slower membrane responses were necessary at low stimulation rates, for both electric and acoustic stimulation. This finding raises the possibility of frequency-dependent differences in neural mechanisms of binaural processing; limitations in ITD sensitivity with bilateral CIs may be due to a mismatch between stimulation rate and cell parameters in ITD-sensitive neurons.

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Deafness-Induced Changes in the Auditory Pathway: Implications for Cochlear Implants

Cited by 172 publications

References 121 publications

Direct Recordings from the Auditory Cortex in a Cochlear Implant User

Direct Recordings from the Auditory Cortex in a Cochlear Implant User

Cochlear implants: A remarkable past and a brilliant future

Modeling Binaural Responses in the Auditory Brainstem to Electric Stimulation of the Auditory Nerve

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