Single-channel versus bilateral multichannel cochlear implant results: a case report.

Pre- and postoperative audiologic findings are compared in a patient who underwent three cochlear implant surgeries: an initial single-channel device in a recently deafened ear with no residual hearing, followed by a multichannel device in a congenitally deafened ear with a severe to profound loss, and subsequent explantation of the single-channel device and reimplantation with a multichannel device.     

Effects of level on nonspectral frequency difference limens for electrical and acoustic stimuli

The purpose of this experiment was to study the effects of stimulus level on discrimination of frequency as represented in the temporal waveforms of acoustic and electrical signals. The subjects were four nonhuman primates in which one ear had been deafened and implanted with an electrode array and the other ear was untreated. Frequency difference limens for 100 Hz electrical sinusoidal stimulation via a cochlear implant in the deafened ear were compared to those for 100 Hz sinusoidally amplitude-modulated white noise (SAM noise) acoustic stimuli to the normal-hearing contralateral ear. To correct for loudness cues, levels of the test stimuli were varied relative to the reference-stimulus level. The test-stimulus levels at which the percent responses were minimum were determined. These levels were used to measure the frequency difference limens. Frequency difference limens for the electrical stimuli decreased as a function of reference-stimulus level through most of the dynamic range, while those for the acoustic stimuli reached a minimum at 20 dB to 40 dB above threshold. For the electrical stimuli the slopes and relative positions of the frequency difference limen vs. level functions varied from subject to subject and with changes in electrode configuration within a subject. These differences were related to threshold level and dynamic range. At higher levels of stimulation, frequency difference limens for acoustic and electrical stimuli fell in the same range. The slopes and relative positions of the frequency difference limen vs. level functions for electrical stimuli did not parallel those of level difference limen vs. level functions collected simultaneously from the same ears. The data suggest that nonspectral frequency discrimination may depend on the number of nerve fibers stimulated. With prostheses in cochleas with less than a full complement of auditory nerve fibers, the data suggest that stimulation level is an important variable influencing discriminability.     

Relationship between distortion product otoacoustic emissions and frequency modulation difference limens

OBJECTIVE: To explore the relationship between distortion product otoacoustic emissions (DPOAEs) and frequency modulation difference limens (FMDLs) in normal-hearing subjects. DESIGN: Fifteen normal-hearing adult subjects (age range = 20 to 29 yr; mean age = 21 yr, 6 mo) participated in the study. Each subject met the following criteria: 1) hearing thresholds <20 dB HL bilaterally at frequencies 0.25 to 8 kHz; 2) type A tympanograms bilaterally; and 3) no history of otologic disease. To reduce gender-related differences, only female subjects were recruited as subjects. DPOAE amplitudes and FMDLs were measured in both ears of 15 female adults at 1, 2, and 4 kHz. Ears were classified on the basis of DPOAE amplitude into large DPOAEs and small DPOAEs. RESULTS: Results indicated that ears with larger DPOAEs showed better frequency discrimination (smaller FMDLs) than did ears with smaller DPOAEs at 2 kHz. CONCLUSIONS: Results of the current study support frequency discrimination models that predict a relationship between frequency selectivity and frequency discrimination.     

Feasibility of multichannel human cochlear nucleus stimulation.

Bipolar electrical stimulation of the brainstem cochlear nucleus (CN) following acoustic tumor removal in an only-hearing ear can provide beneficial hearing. However, the benefits of multichannel stimulation have yet to be defined. Following removal of a second acoustic tumor in a patient with neurofibromatosis 2, a Nucleus mini-22 channel implant device was inserted with the electrode array tip from the foramen of Luschka cephalad along the root entry zone of the eighth nerve, secured by a single suture superficially in the brain stem. Initial stimulation on the sixth postoperative day indicated that electrodes 18 to 22 were capable of CN stimulation without seventh nerve stimulation. Presumed electrode migration precluded further CN stimulation 1 month later. This report illustrates the feasibility of brainstem CN stimulation with an existing multichannel system.     

Characterizing the dependence of pure-tone frequency difference limens on frequency, duration, and level

The purpose of this study was to reveal synaptic plasticity within the dorsal cochlear nucleus (DCN) as a result of noise trauma and to determine whether effective antioxidant protection to the cochlea can also impact plasticity changes in the DCN. Expression of synapse activity markers (synaptophysin and precerebellin) and ultrastructure of synapses were examined in the DCN of chinchilla 10 days after a 105 dB SPL octave-band noise (centered at 4 kHz, 6 h) exposure. One group of chinchilla was treated with a combination of antioxidants (4-hydroxy phenyl N-tert-butylnitrone, N-acetyl-l-cysteine and acetyl-l-carnitine) beginning 4 h after noise exposure. Down-regulated synaptophysin and precerebellin expression, as well as selective degeneration of nerve terminals surrounding cartwheel cells and their primary dendrites were found in the fusiform soma layer in the middle region of the DCN of the noise exposure group. Antioxidant treatment significantly reduced synaptic plasticity changes surrounding cartwheel cells. Results of this study provide further evidence of acoustic trauma-induced neural plasticity in the DCN and suggest that loss of input to cartwheel cells may be an important factor contributing to the emergence of hyperactivity in the DCN after noise exposure. Results further suggest that early antioxidant treatment for acoustic trauma not only rescues cochlear hair cells, but also has impact on central auditory structures.     

Penetrating multichannel stimulation and recording electrodes in auditory prosthesis research

Microelectrode arrays offer the auditory systems physiologists many opportunities through a number of electrode technologies. In particular, silicon substrate electrode arrays offer a large design space including choice of layout plan, range of surface areas for active sites, a choice of site materials and high spatial resolution. Further, most designs can double as recording and stimulation electrodes in the same preparation. Scala tympani auditory prosthesis research has been aided by mapping electrodes in the cortex and the inferior colliculus to assess the CNS responses to peripheral stimulation. More recently silicon stimulation electrodes placed in the auditory nerve, cochlear nucleus and the inferior colliculus have advanced the exploration of alternative stimulation sites for auditory prostheses. Multiplication of results from experimental effort by simultaneously stimulating several locations, or by acquiring several streams of data synchronized to the same stimulation event, is a commonly sought after advantage. Examples of inherently multichannel functions which are not possible with single electrode sites include (1) current steering resulting in more focused stimulation, (2) improved signal-to-noise ratio (SNR) for recording when noise and/or neural signals appear on more than one site and (3) current source density (CSD) measurements. Still more powerful are methods that exploit closely-spaced recording and stimulation sites to improve detailed interrogation of the surrounding neural domain. Here, we discuss thin-film recording/stimulation arrays on silicon substrates. These electrode arrays have been shown to be valuable because of their precision coupled with reproducibility in an ever expanding design space. The shape of the electrode substrate can be customized to accommodate use in cortical, deep and peripheral neural structures while flexible cables, fluid delivery and novel coatings have been added to broaden their application. The use of iridium oxide as the neural interface site material has increased the efficiency of charge transfer for stimulation and lowered impedance for recording electrodes.     

Morphologic and electrophysiologic effects of cochlear implantation and electrical stimulation.

The nondeafened guinea pig model was utilized in this study to assess the functional and morphologic effects of cochlear implantation and electrical stimulation. Auditory brainstem responses (ABRs) were recorded prior to and following intrascalar implantation of a 3M-House cochlear electrode (n = 41 ears), as well as after electrical stimulation (n = 23 ears). The experimental population was divided into the following groups according to implantation and stimulation parameters: 200 microA for 3 hours (group I); 200 microA for 24 hours (group II); 400 microA for 3 hours (group III); implanted, but not stimulated (group IV); and nonimplanted, not stimulated ears (group V). Of those cochleae that sustained the trauma of implantation, 32 percent had no detectable ABR to 110 dB SPL clicks, while only 7 percent additionally failed to respond to 130 dB SPL clicks. No significant difference (one-way ANOVA with repeated measures at the 95 percent confidence limit) could be detected when comparing those ears that retained ABRs according to experimental grouping. Morphologic analysis was performed on 29 cochleae. Spiral ganglion "packing densities" were not found to be significantly different among the groups (ANOVA). The status of the organ of Corti was significantly better in groups II and V in comparison to the other groups (Kruskal-Wallis test with pairwise comparisons, p less than 0.05); there was no discernible dose-response relationship. Morphologic and electrophysiologic changes correlated with insertion trauma and infection rather than with electrical stimulation at the levels tested in this study.(ABSTRACT TRUNCATED AT 250 WORDS)     

Promontory electrical stimulation in postoperative acoustic tumor patients.

Complete deafness can follow acoustic tumor surgery and results from labyrinthine injury, auditory nerve trauma, and/or vascular compromise. A central auditory prosthesis is one potential rehabilitative strategy in such patients. Anatomical studies suggest that some spiral ganglion cells may survive after vascular occlusion, and we have demonstrated responses to electrical stimulation in patients after labyrinthectomy. It was thus hypothesized that patients deafened after a hearing conservation attempt, but maintaining an intact auditory nerve, could utilize an intracochlear implant. To investigate this possibility, promontory electrical stimulation was performed on three patients who had tumors less than 2 cm and who had serviceable preoperative hearing, but no responses postoperatively. Behavioral responses and electrically evoked auditory brainstem and middle latency responses were obtained from two patients, one of whom was 6 years postsurgery. These data indicate that a cochlear implant may be possible after acoustic tumor surgery.     

Grafting and electrical stimulation of the auditory nerve in cats.

The effect of implanting wire electrodes into the cochlea is limited by the deficit of nerve fibers in most diseases of the cochlea. Therefore, in a series of experiments it was tried, for the first time, to direct new outspreading nerve fibres into the afferent acoustic nerve by grafting a motor nerve to it. A second series of experiments should demonstrate the possibility of direct electrical stimulation of the eighs nerve by implanting wire electrodes via the transoccipital approach. The electrically evoked potentials, recorded at the auditory cortex, were compaired to potentials evoked by auditory stimulation. The answers to acoustic or electric stimulation showed no significant difference.     

Effects of channel number and place of stimulation on performance with the Cochlear Corporation multichannel implant.

The effects of active channel number and place of stimulation on auditory-only performance with the Cochlear Corporation multichannel cochlear implant were investigated in seven subjects. A balanced crossover design was employed; subjects were initially programmed with either 10 basal or the full complement of 20 to 21 active electrodes. Following a 6-month period with the initial coding strategy, subjects were programmed with the alternate configuration, which they used for an additional 6 months. Auditory-only performance on suprasegmental, phoneme (vowel and consonant) open- and closed-set speech recognition was compared between the two electrode configurations. Additionally, performance with the first configuration and performance with the second configuration 3 days following programming were also compared. While a trend for increased scores was noted with 20 electrodes, especially with open-set speech recognition tasks, none of the differences between the two configurations reached statistical significance, as indicated by a Wilcoxon test. A comparison of performance at the end of the first 6-month period and 3 days following programming with the second configuration revealed a trend for reduced scores, especially on vowel tests. Overall, our results indicate that the feature extraction coding strategy associated with the Cochlear Corporation device allows patients to function well with only 10 basal electrodes and that speech recognition is only mildly affected initially when patients are programmed with a different encoding strategy.     

Promontory electrical stimulation in labyrinthectomized ears

Bilateral deafness can occur in patients with Menière's disease who have undergone a labyrinthectomy in one ear. To investigate the feasibility of a cochlear implant in the labyrinthectomized ear, promontory electrical testing by transtympanic needle was performed in six patients who had undergone a unilateral transmastoid labyrinthectomy 6 weeks to 5 years previously. All patients had a behavioral response to the stimulus, and each described a different pitch percept with the four frequencies used. Five of the patients demonstrated an electrically evoked middle latency response. These data are comparable with behavioral and electrophysiologic responses from ears deafened by other causes and now successfully implanted. The results suggest that peripheral neural elements and central auditory pathways remain at least partially functional many years after a labyrinthectomy. Thus, a labyrinthectomy should not be withheld as a surgical option if otherwise indicated.     

Transdermal electrical stimulation in sensorineural tinnitus

In 73 patients composing 84 ears, with persistent decompensated tinnitus and sensorineural deafness, tinnitus suppression was attempted with low frequency, low ampere transdermal electrical stimulation (TDES). The causes of tinnitus were presbyacusis, unknown aetiology, Noise exposure, otosclerosis, ototoxic drugs, Endolymphatic hydrops, labyrinthitis and post head injury. Reduction of tinnitus was achieved in 38 of 84 ears. Results were achieved in patients with the following order. 1) Unknown aetiology 53.3% 2) Ototoxic drugs 50% 3) Presbyacusis 45% 4) Labyrinthitis 40% 5) Post head injury, Endolymphatic hydrops & otosclerosis 33.3% each. The lasting effect of the tinnitus suppression varied from few hours to few weeks. Effective reduction could be re-achieved by re-stimulation.     

Tinnitus reduction using transcutaneous electrical stimulation

Electrical stimulation as a treatment for tinnitus seems to be effective in about 50% of patients with tinnitus of various causes. Electrical stimulation as a treatment for tinnitus is safe, if delivered within the parameters described in this article.     

Compositional difference in middle ear effusion: mucous versus serous.

OBJECTIVES: Serous otitis media is usually responsive to medical treatment, whereas mucoid otitis media is not. The present study was undertaken to elucidate the compositional difference between serous and mucoid effusion and to investigate whether MUC5AC acts as a major mucin in the middle ear mucosa with mucoid otitis media. STUDY DESIGN: This study involved a chemical analysis of middle ear effusion and immunostaining of the middle ear mucosa. METHODS: Middle ear effusion samples were collected from 27 patients with mucoid otitis media and 18 patients with serous otitis media. The levels of mucin, lysozyme, secretory immunoglobulin A, and interleukin-8 were measured by dot blotting or enzyme-linked immunosorbent assay. Periodic acid-Schiff and immunohistochemical staining with monoclonal anti-MUC5AC antibody were performed on the serial sections of middle ear mucosa with mucoid otitis media. RESULTS: Mucoid effusions contained higher levels of mucin, lysozyme, secretory immunoglobulin A, and interleukin-8 than did serous effusions. Immunohistological study revealed that MUC5AC mucin was expressed in only a small portion of the goblet cells of middle ear mucosa with mucoid otitis media. CONCLUSIONS: The study suggests that both serous secretions and mucin might make the middle ear effusion more viscous and that mucins other than MUC5AC might have a major role in the viscosity of middle ear effusion. Further study is necessary to identify the major mucins in the middle ear effusion of otitis media with effusion.