Acoustic Hearing After Murine Cochlear Implantation: Effects of Trauma and Implant Type.

Objectives: To model the contribution of implant material and insertion trauma on loss of acoustic hearing after cochlear implantation in an appropriate animal model.

Methods: Sixty-five C57Bl/6J mice underwent unilateral implantation with implant grade materials: 2 implant grade silicones and a third uncoated platinum wire. A sham surgery group was included as a control.

Mouse cochleostomy: a minimally invasive dorsal approach for modeling cochlear implantation.

Objectives/hypothesis: The murine model has been used extensively to model and study human deafness. Technical difficulty in the surgical approach due to the small size of the tympanic bulla and a robust stapedial artery has limited its application for studies of cochlear implantation and electrical stimulation. We describe a minimally traumatic, stapedial artery-sparing approach to the round window that may be used to access the mouse cochlea for acute or chronic studies of implantation and stimulation.

Neural masking by sub-threshold electric stimuli: animal and computer model results.

Electric stimuli can prosthetically excite auditory nerve fibers to partially restore sensory function to individuals impaired by profound or severe hearing loss. While basic response properties of electrically stimulated auditory nerve fibers (ANF) are known, responses to complex, time-changing stimuli used clinically are inadequately understood. We report that forward-masker pulse trains can enhance and reduce ANF responsiveness to subsequent stimuli and the novel observation that sub-threshold (nonspike-evoking) electric trains can reduce responsiveness to subsequent pulse-train stimuli.

Changes in auditory nerve responses across the duration of sinusoidally amplitude-modulated electric pulse-train stimuli.

Response rates of auditory nerve fibers (ANFs) to electric pulse trains change over time, reflecting substantial spike-rate adaptation that depends on stimulus parameters. We hypothesize that adaptation affects the representation of amplitude-modulated pulse trains used by cochlear prostheses to transmit speech information to the auditory system. We recorded cat ANF responses to sinusoidally amplitude-modulated (SAM) trains with 5,000 pulse/s carriers.

Auditory nerve fiber responses to combined acoustic and electric stimulation.

Persons with a prosthesis implanted in a cochlea with residual acoustic sensitivity can, in some cases, achieve better speech perception with "hybrid" stimulation than with either acoustic or electric stimulation presented alone. Such improvements may involve "across auditory-nerve fiber" processes within central nuclei of the auditory system and within-fiber interactions at the level of the auditory nerve. Our study explored acoustic-electric interactions within feline auditory nerve fibers (ANFs) so as to address two goals.

Effects of temporal properties on compound action potentials in response to amplitude-modulated electric pulse trains in guinea pigs.

The electrically evoked compound action potential (ECAP) of the auditory nerve in response to amplitude-modulated pulse trains varies over time, but the response amplitudes are not linearly proportional to the level of stimulus pulses. At least two mechanisms could contribute to the deviations of the ECAP response pattern from that of the stimulus envelope. The first mechanism is time-invariant or stationary that reflects the non-linear growth of response amplitude with changes in stimulus level that is evident in the response to single pulses.

Changes across time in the temporal responses of auditory nerve fibers stimulated by electric pulse trains.

Most auditory prostheses use modulated electric pulse trains to excite the auditory nerve. There are, however, scant data regarding the effects of pulse trains on auditory nerve fiber (ANF) responses across the duration of such stimuli. We examined how temporal ANF properties changed with level and pulse rate across 300-ms pulse trains.

Electrically evoked auditory steady-state responses in a guinea pig model: latency estimates and effects of stimulus parameters.

Cochlear implant speech processors typically extract envelope information of speech signals for presentation to the auditory nerve as modulated trains of electric pulses. Recent studies showed the feasibility of recording, at the scalp, the electrically evoked auditory steady-state response using amplitude-modulated electric stimuli. Sinusoidally amplitude-modulated electric stimuli were used to elicit such responses from guinea pigs in order to characterize this response.

Acoustic-electric interactions in the guinea pig auditory nerve: simultaneous and forward masking of the electrically evoked compound action potential.

The study investigated the time course of the effects of acoustic and electric stimulation on the electrically evoked compound action potential (ECAP). Adult guinea pigs were used in acute experimental sessions. Bursts of acoustic noise and high-rate (5000 pulses/s) electric pulse trains were used as maskers.

Prosurvival and proapoptotic intracellular signaling in rat spiral ganglion neurons in vivo after the loss of hair cells.

Neurons depend on afferent input for survival. Rats were given daily kanamycin injections from P8 to P16 to destroy hair cells, the sole afferent input to spiral ganglion neurons (SGNs). Most SGNs die over an approximately 14-week period after deafferentation.

Changes across time in spike rate and spike amplitude of auditory nerve fibers stimulated by electric pulse trains.

We undertook a systematic evaluation of spike rates and spike amplitudes of auditory nerve fiber (ANF) responses to trains of electric current pulses. Measures were obtained from acutely deafened cats to examine time-related changes free from the effects of hair-cell and synaptic adaptation. Such data relate to adaptation that likely occurs in ANFs of cochlear-implant users.

Binaural interactions of electrically and acoustically evoked responses recorded from the inferior colliculus of guinea pigs.

Binaural interactions within the inferior colliculus (IC) elicited by electric and acoustic stimuli were investigated in this study. Using a guinea pig model, binaural acoustic stimuli were presented with different time delays, as were combinations of binaural electric and acoustic stimuli. Averaged evoked potentials were measured using electrodes inserted into the central nucleus of the IC to obtain the binaural interaction component (BIC), computed by subtracting the sum of the two monaural responses from the binaural response.

Selective cochlear degeneration in mice lacking the F-box protein, Fbx2, a glycoprotein-specific ubiquitin ligase subunit.

Little is known about the role of protein quality control in the inner ear. We now report selective cochlear degeneration in mice deficient in Fbx2, a ubiquitin ligase F-box protein with specificity for high-mannose glycoproteins (Yoshida et al., 2002).

Electrically evoked auditory steady-state responses in Guinea pigs.

Most cochlear implant systems available today provide the user with information about the envelope of the speech signal. The goal of this study was to explore the feasibility of recording electrically evoked auditory steady-state response (ESSR) and in particular to evaluate the degree to which the response recorded using electrical stimulation could be separated from stimulus artifact. Sinusoidally amplitude-modulated electrical stimuli with alternating polarities were used to elicit the response in adult guinea pigs.

Electrical excitation of the acoustically sensitive auditory nerve: single-fiber responses to electric pulse trains.

Nearly all studies on auditory-nerve responses to electric stimuli have been conducted using chemically deafened animals so as to more realistically model the implanted human ear that has typically been profoundly deaf. However, clinical criteria for implantation have recently been relaxed. Ears with "residual" acoustic sensitivity are now being implanted, calling for the systematic evaluation of auditory-nerve responses to electric stimuli as well as combined electric and acoustic stimuli in acoustically sensitive ears.

Effects of acoustic noise on the auditory nerve compound action potentials evoked by electric pulse trains.

This study investigated the effects of acoustic noise on the auditory nerve compound action potentials in response to electric pulse trains. Subjects were adult guinea pigs, implanted with a minimally invasive electrode to preserve acoustic sensitivity. Electrically evoked compound action potentials (ECAP) were recorded from the auditory nerve trunk in response to electric pulse trains both during and after the presentation of acoustic white noise.

Intracochlear and extracochlear ECAPs suggest antidromic action potentials.

With experimental animals, the electrically evoked compound action potential (ECAP) can be recorded from multiple sites (e.g., round window, intracranial and intracochlear sites).

Feasibility of using silicon-substrate recording electrodes within the auditory nerve.

The use of penetrating, silicon-substrate (i.e., "thin-film") probes within a cross-section of a sensory nerve offers the possibility of assessing the pattern and extent of fiber excitation within the nerve.

Response of the auditory nerve to sinusoidal electrical stimulation: effects of high-rate pulse trains.

Electrical stimulation of the auditory nerve produces highly synchronized responses. As a consequence, electrical stimulation may result in a narrow dynamic range of hearing and poor temporal representation of an input signal. The electrically evoked compound action potential (ECAP) is an electrophysiologic response used for neural assessment in individuals with auditory prostheses.

Auditory response to intracochlear electric stimuli following furosemide treatment.

The influence of functional hair cells on electrical stimulation of the auditory nerve is an important issue as individuals with significant residual hearing are now cochlear implant candidates. Previous work has shown that chemical deafening during the course of acute experiments changes the auditory nerve's responses to electrical stimulation [Third Quarterly Progress Report, NIH contract N01-DC-9-2106 (2000), Final Report, NIH Contract N01-DC-9-2106 (2002)]. This study extended that work by investigating the changes and subsequent recovery following furosemide injections which reversibly impair hair-cell function [Hear.

Electrode configuration influences action potential initiation site and ensemble stochastic response properties.

The configuration of intracochlear electrodes used to electrically stimulate the auditory nerve influences the ensemble fiber response. For example, monopolar stimulation produces lower thresholds and greater spread of excitation than does bipolar stimulation. We used two approaches to investigate how the ensemble of auditory-nerve fibers responds to stimulation delivered by different electrode configurations.