Dissociated Representation of Binaural Cues in Single-Sided Deafness: Implications for Cochlear Implantation.

Congenital single-sided deafness (SSD) leads to an aural preference syndrome that is characterized by overrepresentation of the hearing ear in the auditory system. Cochlear implantation (CI) of the deaf ear is an effective treatment for SSD. However, the newly introduced auditory input in congenital SSD often does not reach expectations in late-implanted CI recipients with respect to binaural hearing and speech perception.

Congenital deafness reduces alpha-gamma cross-frequency coupling in the auditory cortex.

Neurons within a neuronal network can be grouped by bottom-up and top-down influences using synchrony in neuronal oscillations. This creates the representation of perceptual objects from sensory features. Oscillatory activity can be differentiated into stimulus-phase-locked (evoked) and non-phase-locked (induced).

Factors influencing the relationship between cochlear health measures and speech recognition in cochlear implant users.

Background: One factor which influences the speech intelligibility of cochlear implant (CI) users is the number and the extent of the functionality of spiral ganglion neurons (SGNs), referred to as "cochlear health." To explain the interindividual variability in speech perception of CI users, a clinically applicable estimate of cochlear health could be insightful. The change in the slope of the electrically evoked compound action potentials (eCAP), amplitude growth function (AGF) as a response to increased interphase gap (IPG) (IPGE) has been introduced as a potential measure of cochlear health.

Deficient Recurrent Cortical Processing in Congenital Deafness.

The influence of sensory experience on cortical feedforward and feedback interactions has rarely been studied in the auditory cortex. Previous work has documented a dystrophic effect of deafness in deep cortical layers, and a reduction of interareal couplings between primary and secondary auditory areas in congenital deafness which was particularly pronounced in the top-down direction (from the secondary to the primary area). In the present study, we directly quantified the functional interaction between superficial (supragranular, I to III) and deep (infragranular, V and VI) layers of feline's primary auditory cortex A1, and also between superficial/deep layers of A1 and a secondary auditory cortex, namely the posterior auditory field (PAF).

Deafness Weakens Interareal Couplings in the Auditory Cortex.

The function of the cerebral cortex essentially depends on the ability to form functional assemblies across different cortical areas serving different functions. Here we investigated how developmental hearing experience affects functional and effective interareal connectivity in the auditory cortex in an animal model with years-long and complete auditory deprivation (deafness) from birth, the congenitally deaf cat (CDC). Using intracortical multielectrode arrays, neuronal activity of adult hearing controls and CDCs was registered in the primary auditory cortex and the secondary posterior auditory field (PAF).

Band-Limited Chirp-Evoked Compound Action Potential in Guinea Pig: Comprehensive Neural Measure for Cochlear Implantation Monitoring.

Objectives: Patients with severely impaired high-frequency hearing and sufficient residual low-frequency hearing can be provided with a cochlear implant (CI), thereby facilitating ipsilateral electric and acoustic stimulation with established advantages over electric stimulation alone. However, partial or complete hearing loss often occurred after implantation due to, inter alia, acute mechanical trauma to cochlear structures during electrode insertion. Possibilities of intraoperative monitoring using electrocochleography (ECochG) have recently been studied in CI patients, primarily using the ongoing response to low-frequency tone bursts consisting of the cochlear microphonic (CM) and the auditory nerve neurophonic.

Long-Term Release Profile of Dexamethasone-Loaded Silicone Rods Implanted Into the Cochlea of Guinea Pigs.

Glucocorticoids are used intra-operatively in cochlear implant surgeries to reduce the inflammatory reaction caused by insertion trauma and the foreign body response against the electrode carrier after cochlear implantation. To prevent higher systemic concentrations of glucocorticoids that might cause undesirable systemic side effects, the drug should be applied locally. Since rapid clearance of glucocorticoids occurs in the inner ear fluid spaces, sustained application is supposedly more effective in suppressing foreign body and tissue reactions and in preserving neuronal structures.

Induced cortical responses require developmental sensory experience.

Sensory areas of the cerebral cortex integrate the sensory inputs with the ongoing activity. We studied how complete absence of auditory experience affects this process in a higher mammal model of complete sensory deprivation, the congenitally deaf cat. Cortical responses were elicited by intracochlear electric stimulation using cochlear implants in adult hearing controls and deaf cats.

Physiological Mechanisms in Combined Electric-Acoustic Stimulation.

Objective: Electrical stimulation is normally performed on ears that have no hearing function, i.e., lack functional hair cells.

Cross-Modal Plasticity in Higher-Order Auditory Cortex of Congenitally Deaf Cats Does Not Limit Auditory Responsiveness to Cochlear Implants.

Unlabelled: Congenital sensory deprivation can lead to reorganization of the deprived cortical regions by another sensory system. Such cross-modal reorganization may either compete with or complement the "original" inputs to the deprived area after sensory restoration and can thus be either adverse or beneficial for sensory restoration. In congenital deafness, a previous inactivation study documented that supranormal visual behavior was mediated by higher-order auditory fields in congenitally deaf cats (CDCs).

Monaural Congenital Deafness Affects Aural Dominance and Degrades Binaural Processing.

Cortical development extensively depends on sensory experience. Effects of congenital monaural and binaural deafness on cortical aural dominance and representation of binaural cues were investigated in the present study. We used an animal model that precisely mimics the clinical scenario of unilateral cochlear implantation in an individual with single-sided congenital deafness.

Strengthening of hearing ear representation reduces binaural sensitivity in early single-sided deafness.

Single-sided deafness initiates extensive adaptations in the central auditory system, with the consequence that a stronger and a weaker ear representation develops in the auditory brain. Animal studies demonstrated that the effects are substantially stronger if the condition starts early in development. Sequential binaural cochlear implantations with longer interimplant delays demonstrate that the speech comprehension at the weaker ear is substantially compromised.

Electric-acoustic interactions in the hearing cochlea: single fiber recordings.

The present study investigates interactions of simultaneous electric and acoustic stimulation in single auditory nerve fibers in normal hearing cats. First, the auditory nerve was accessed with a microelectrode and response areas of single nerve fibers were determined for acoustic stimulation. Second, response thresholds to extracochlear sinusoidal electric stimulation using ball electrodes positioned at the round window were measured.

Unilateral hearing during development: hemispheric specificity in plastic reorganizations.

The present study investigates the hemispheric contributions of neuronal reorganization following early single-sided hearing (unilateral deafness). The experiments were performed on ten cats from our colony of deaf white cats. Two were identified in early hearing screening as unilaterally congenitally deaf.

Single-sided deafness leads to unilateral aural preference within an early sensitive period.

Unilateral deafness has a high incidence in children. In addition to children who are born without hearing in one ear, children with bilateral deafness are frequently equipped only with one cochlear implant, leaving the other ear deaf. The present study investigates the effects of such single-sided deafness during development in the congenitally deaf cat.

Development of brainstem-evoked responses in congenital auditory deprivation.

To compare the development of the auditory system in hearing and completely acoustically deprived animals, naive congenitally deaf white cats (CDCs) and hearing controls (HCs) were investigated at different developmental stages from birth till adulthood. The CDCs had no hearing experience before the acute experiment. In both groups of animals, responses to cochlear implant stimulation were acutely assessed.

Protection of inner ear function after cochlear implantation: compound action potential measurements after local application of glucocorticoids in the guinea pig cochlea.

Background: Cochlear implant users with residual hearing often benefit greatly from simultaneous electric and acoustic stimulation. However, implantation can cause trauma to the inner ear, resulting in poorer hearing postoperatively. We investigated whether a single local injection of glucocorticoids can reduce hearing loss in long-term implanted guinea pigs.

Electric-acoustic stimulation of the auditory system: a review of the first decade.

Electric-acoustic stimulation (EAS) was developed for individuals with a profound hearing loss in the high frequencies and a substantial residual low-frequency hearing (LFH). For this group of candidates, conventional hearing aids often neither provided sufficient amplification nor were they considered suitable for cochlear implantation due to the possible destruction of residual hearing capabilities. With EAS, combining electric stimulation with an ipsilateral acoustic stimulation, preservation of residual LFH and the development of a new speech processor uniting both strategies became essential.

Neuronal responses in cat inferior colliculus to combined acoustic and electric stimulation.

The present study explored the interactions of combined electric and acoustic stimulation (EAS) on neural responses in the central auditory system. Normal-hearing cats were implanted unilaterally with scala tympani electrodes. Two experimental approaches were used.

Cortical representation of interaural time difference in congenital deafness.

Binaural cues are required for localization of sound sources. In the present paper, representation of binaural cues has been investigated in the adult auditory cortex. Hearing and congenitally deaf cats were stimulated through binaural cochlear implants and unit responses were collected in the subregion of field A1 showing the largest amplitudes of evoked local field potentials.

Spatiotemporal patterns of cortical activity with bilateral cochlear implants in congenital deafness.

Congenital deafness affects developmental processes in the auditory cortex. In this study, local field potentials (LFPs) were mapped at the cortical surface with microelectrodes in response to cochlear implant stimulation. LFPs were compared between hearing controls and congenitally deaf cats (CDCs).

Application of a corticosteroid (Triamcinolon) protects inner ear function after surgical intervention.

Hypothesis: Opening of the inner ear during stapes surgery or cochlear implantation may result in trauma to inner ear structures and possible hearing loss. The dual aim of the present study was to evaluate the effectiveness of locally applied Triamcinolon* to protect the inner ear against surgically induced trauma and to exclude possible ototoxic effects.

Methods: In an animal model (guinea pig), a corticosteroid (Triamcinolon) was topically applied to the inner ear, either by extracochlear application and diffusion through the round window membrane or by direct intracochlear application via a cochleostomy.

Protecting the cochlea during stapes surgery: is there a role for corticosteroids?

The aim of the present study was to evaluate possible protective effects of corticosteroids on the inner ear after surgical trauma and to exclude any ototoxicity. A corticosteroid (triamcinolone, Volon A) was topically applied to the inner ear of guinea pigs, either by extracochlear application with permeation and diffusion through the round window membrane or by intracochlear application with direct infusion into the inner ear via a cochleostomy. Threshold and input/output functions of compound action potentials (CAPs) were determined before and after application of the corticosteroid.