Deafness alters auditory nerve fibre responses to cochlear implant stimulation (original) (raw)
Related papers
Journal of Neurophysiology, 2010
Neural prostheses, such as cochlear and retinal implants, induce perceptual responses by electrically stimulating sensory nerves. These devices restore sensory system function by using patterned electrical stimuli to evoke neural responses. An understanding of their function requires knowledge of the nerves responses to relevant electrical stimuli as well as the likely effects of pathology on nerve function. We describe how sensorineural hearing loss (SNHL) affects the response properties of single auditory nerve fibers (ANFs) to electrical stimuli relevant to cochlear implants. The response of 188 individual ANFs were recorded in response to trains of stimuli presented at 200, 1,000, 2,000, and 5,000 pulse/s in acutely and chronically deafened guinea pigs. The effects of stimulation rate and SNHL on ANF responses during the 0–2 ms period following stimulus onset were examined to minimize the influence of ANF adaptation. As stimulation rate increased to 5,000 pulse/s, threshold decr...
Hearing Research, 2011
Criteria for cochlear implantation keep expanding and people with substantial residual low-frequency hearing are considered candidates for implantation nowadays. Therefore, electro-acoustical stimulation in the same ear (EAS) is receiving increasing interest. We have investigated the effects of intracochlear electrical stimulation on acoustically evoked auditory-nerve activity, using a forward masking paradigm. The stimulation electrode was placed in the basal turn of the cochlea. Compound action potential (CAP) recordings were performed in guinea pigs with severe high-frequency hearing loss and in normalhearing control animals. In normal-hearing animals, electrical stimulation generally suppressed CAPs, especially at high acoustic frequencies (8 and 16 kHz) and low sound levels. At low frequencies (0.5 and 1 kHz), suppression was observed only at high sound levels. In animals with a high-frequency hearing loss, suppression of CAPs at low frequencies was substantially less compared to control animals, even at high current levels and temporal overlap of acoustic and electric stimuli. Hence, effects of electrical stimulation substantially differed between normal-hearing animals and animals with a high-frequency hearing loss. These findings stress the need for a proper animal model when investigating EAS. We conclude that in case of high-frequency loss, the basal part of the cochlea can be stimulated electrically with little effect on responses to low-frequency acoustic stimuli.
The Annals of otology, rhinology, and laryngology, 2002
Bilateral cochlear implantation provides an interesting model for in vivo study of the effect of long-term profound deafness on neural transmission. We present electrophysiological observations on 2 patients implanted with the MXM Binaural Digisonic Convex system. This uncommon design consists of 2 electrode arrays placed bilaterally into the scala tympani and controlled by a single speech processor. In both patients, the duration of deafness before cochlear implantation clearly differed from one ear to the other. Electrically evoked auditory brain stem responses (EABRs) were measured and the EABRs from the ear with the longer deafness duration showed a lengthening of wave V latency. In I patient, recordings from this ear also showed a lack of reproducibility of wave III. The data suggest that neural responsiveness in the peripheral and intermediate auditory pathways is adversely affected by deafness duration. Poor EABRs on one ear possibly result from the total duration of deafness...
We investigated the effect of pulse duration (PD) and interphase-gap (IPG) on the electrically-evoked auditory brain stem response (EABR) and viiith nerve compound action potential (ECAP) of deafened guinea pigs in order to test the hypothesis that the extent of change in these neural responses is affected by the histological status of the auditory nerve. Fifteen guinea pigs were deafened by co-administration of kanamycin and furosemide. Animals were acutely implanted with an 8-band electrode array at 1, 4 or 12 weeks following deafening. EABR and ECAP input/output functions were recorded in response to charge balanced biphasic current pulses. We determined the change in current required to equalize; (i) the EABR amplitude when the duration of the current pulse was doubled (104-208 micros/phase); and (ii) the EABR and ECAP amplitudes when the IPG was increased from 8 to 58 micros using a 104 micros/phase current pulse. Following the completion of each experiment the cochleae were examined quantitatively for spiral ganglion neuron survival. As expected, the current level required to evoke an EABR with equal amplitude was lower when the animal was stimulated with current pulses of 208 compared with 104 micros/phase. Moreover, the current level required to evoke EABR/ECAPs with equal amplitude was lower when current pulses had an IPG of 58 versus 8 micros. Importantly, there was a reduction in the magnitude of this effect with greater neural loss; the reduced efficacy of changing both PD and IPG on these electrically-evoked potentials was statistically correlated with neural survival. These results may provide a tool for investigating the contribution of auditory nerve survival to clinical performance among cochlear implant subjects.
Hearing Research, 2006
We investigated the effect of pulse duration (PD) and interphase-gap (IPG) on the electrically-evoked auditory brain stem response (EABR) and viii th nerve compound action potential (ECAP) of deafened guinea pigs in order to test the hypothesis that the extent of change in these neural responses is affected by the histological status of the auditory nerve. Fifteen guinea pigs were deafened by coadministration of kanamycin and furosemide. Animals were acutely implanted with an 8-band electrode array at 1, 4 or 12 weeks following deafening. EABR and ECAP input/output functions were recorded in response to charge balanced biphasic current pulses. We determined the change in current required to equalize; (i) the EABR amplitude when the duration of the current pulse was doubled (104 to 208 μs/phase); and (ii) the EABR and ECAP amplitudes when the IPG was increased from 8 μs to 58 μs using a 104 μs/phase current pulse. Following the completion of each experiment the cochleae were examined quantitatively for spiral ganglion neuron survival. As expected, the current level required to evoke an EABR with equal amplitude was lower when the animal was stimulated with current pulses of 208 compared with 104 μs/phase. Moreover, the current level required to evoke EABR/ECAPs with equal amplitude was lower when current pulses had an IPG of 58 versus 8 μs. Importantly, there was a reduction in the magnitude of this effect with greater neural loss; the reduced efficacy of changing both PD and IPG on these electrically-evoked potentials was statistically correlated with neural survival. These results may provide a tool for investigating the contribution of auditory nerve survival to clinical performance among cochlear implant subjects.
Journal of the Association for Research in Otolaryngology, 2014
After severe hair cell loss, secondary degeneration of spiral ganglion cells (SGCs) is observed-a gradual process that spans years in humans but only takes weeks in guinea pigs. Being the target for cochlear implants (CIs), the physiological state of the SGCs is important for the effectiveness of a CI. For assessment of the nerve's state, focus has generally been on its response threshold. Our goal was to add a more detailed characterization of SGC functionality. To this end, the electrically evoked compound action potential (eCAP) was recorded in normal-hearing guinea pigs and guinea pigs that were deafened 2 or 6 weeks prior to the experiments. We evaluated changes in eCAP characteristics when the phase duration (PD) and inter-phase gap (IPG) of a biphasic current pulse were varied. We correlated the magnitude of these changes to quantified histological measures of neurodegeneration (SGC packing density and SGC size). The maximum eCAP amplitude, derived from the input-output function, decreased after deafening, and increased with both PD and IPG. The eCAP threshold did not change after deafening, and decreased with increasing PD and IPG. The dynamic range was wider for the 6-weeks-deaf animals than for the other two groups. Excitability increased with IPG (steeper slope of the input-output function and lower stimulation level at the half-maximum eCAP amplitude), but to a lesser extent for the deafened animals than for normal-hearing controls. The latency was shorter for the 6-weeks-deaf animals than for the other two groups. For several of these eCAP characteristics, the effect size of IPG correlated well with histological measures of degeneration, whereas effect size of PD did not. These correlations depend on the use of high current levels, which could limit clinical application. Nevertheless, their potential of these correlations towards assessment of the condition of the auditory nerve may be of great benefit to clinical diagnostics and prognosis in cochlear implant recipients.
Effects of Hearing Preservation on Psychophysical Responses to Cochlear Implant Stimulation
Journal of the Association for Research in Otolaryngology, 2010
Previous studies have shown that residual acoustic hearing supplements cochlear implant function to improve speech recognition in noise as well as perception of music. The current study had two primary objectives. First, we sought to determine how cochlear implantation and electrical stimulation over a time period of 14 to 21 months influence cochlear structures such as hair cells and spiral ganglion neurons. Second, we sought to investigate whether the structures that provide acoustic hearing also affect the perception of electrical stimulation. We compared psychophysical responses to cochlear implant stimulation in two groups of adult guinea pigs. Group I (11 animals) received a cochlear implant in a previously untreated ear, while group II (ten animals) received a cochlear implant in an ear that had been previously infused with neomycin to destroy hearing. Psychophysical thresholds were measured in response to pulse-train and sinusoidal stimuli. Histological analysis of all group I animals and a subset of group II animals was performed. Nine of the 11 group I animals showed survival of the organ of Corti and spiral ganglion neurons adjacent to the electrode array. All group I animals showed survival of these elements in regions apical to the electrode array. Group II animals that were examined histologically showed complete loss of the organ of Corti in regions adjacent and apical to the electrode array and severe spiral ganglion neuron loss, consistent with previous reports for neomycin-treated ears. Behaviorally, group II animals had significantly lower thresholds than group I animals in response to 100 Hz sinusoidal stimuli. However, group I animals had significantly lower thresholds than group II animals in response to pulse-train stimuli (0.02 ms/phase; 156 to 5,000 pps). Additionally, the two groups showed distinct threshold versus pulse rate functions. We hypothesize that the differences in detection thresholds between groups are caused by the electrical activation of the hair cells in group I animals and/or differences between groups in the condition of the spiral ganglion neurons.
Brain Sciences
The cochlear implant (CI) is the most successful neuroprosthesis allowing thousands of patients with profound hearing loss to recover speech understanding. Recently, cochlear implants have been proposed to subjects with residual hearing and, in these cases, shorter CIs were implanted. To be successful, it is crucial to preserve the patient’s remaining hearing abilities after the implantation. Here, we quantified the effects of CI insertion on the responses of auditory cortex neurons in anesthetized guinea pigs. The responses of auditory cortex neurons were determined before and after the insertion of a 300 µm diameter CI (six stimulating electrodes, length 6 mm). Immediately after CI insertion there was a 5 to 15 dB increase in the threshold for cortical neurons from the middle to the high frequencies, accompanied by a decrease in the evoked firing rate. Analyzing the characteristic frequency (CF) values revealed that in large number of cases, the CFs obtained after insertion were l...
Protective Effects of Patterned Electrical Stimulation on the Deafened Auditory System
2005
This Quarterly Progress Report presents a summary of some of the findings from psychophysical studies conducted in neonatally deafened cats to examine auditory detection and discrimination thresholds for complex signals. A detailed report and full discussion of these and other findings is currently in press in the Journal of Neurophysiology. To explore the basic mechanisms underlying the success of contemporary speech processing strategies for cochlear implant recipients, this work examined how specific complex electrical stimuli delivered by intracochlear electrodes are processed in the central auditory system. Sinusoidal amplitude modulated (SAM) and unmodulated pulse trains were used to investigate behavioral and central neuronal thresholds in the same deaf cats. Some animals were trained in a discrimination task to respond to changes in the modulation frequency of successive SAM signals. The study had four primary objectives: 1) to estimate psychophysical thresholds for SAM and unmodulated pulse trains in the same trained animals; 2) to determine neural thresholds for SAM and unmodulated pulse trains; 3) to compare psychophysical and neural thresholds in the same animal; and 4) to evaluate the ability of animals to discriminate changes in the modulation frequency of SAM signals delivered by a cochlear implant.