Standard Cochlear Implantation Research Articles

Neural correlates of speech in noise perception differences between combined electric-acoustic stimulation and standard cochlear implants

Cochlear implants have evolved to utilize residual acoustic hearing that combines to electric stimulation, known as electric-acoustic stimulation (EAS). However, there are mixed expectations about the benefits of EAS. A positive perspective expects that contributions from residual hearing provide better access to acoustic cues that is helpful for speech-in-noise perception. An opposing view concerns potentially poorer spectral resolution of EAS electrodes’ stimulation as those electrodes are often inserted close to lateral wall, which may cause poorer speech-in-noise perception. This study aimed to directly compare neural processes of speech-in-noise perception between EAS and standard CI users to provide an answer to the above alternative expectations. We used 64-channel EEG to measure cortical evoked responses to (1) background noise and (2) target word while listeners perform a word-in-noise task. Then, we compared the amplitude ratio of evoked responses to the target word and background noise, referred to as “internal SNR,” which reflects how well target sound is unmasked from the mixture of speech and noise. Based on the comparison of 55 EAS and 22 standard CI users, internal SNR was significantly larger in EAS CI users. This result indicates that EAS provides enhanced neural processes for speech unmasking.

Direct Cochlear Recordings in Humans Show a Theta Rhythmic Modulation of Auditory Nerve Activity by Selective Attention.

The architecture of the efferent auditory system enables prioritization of strongly overlapping spatiotemporal cochlear activation patterns elicited by relevant and irrelevant inputs. So far, attempts at finding such attentional modulations of cochlear activity delivered indirect insights in humans or required direct recordings in animals. The extent to which spiral ganglion cells forming the human auditory nerve are sensitive to selective attention remains largely unknown. We investigated this question by testing the effects of attending to either the auditory or visual modality in human cochlear implant (CI) users (3 female, 13 male). Auditory nerve activity was directly recorded with standard CIs during a silent (anticipatory) cue-target interval. When attending the upcoming auditory input, ongoing auditory nerve activity within the theta range (5-8 Hz) was enhanced. Crucially, using the broadband signal (4-25 Hz), a classifier was even able to decode the attended modality from single-trial data. Follow-up analysis showed that the effect was not driven by a narrow frequency in particular. Using direct cochlear recordings from deaf individuals, our findings suggest that cochlear spiral ganglion cells are sensitive to top-down attentional modulations. Given the putatively broad hair-cell degeneration of these individuals, the effects are likely mediated by alternative efferent pathways compared with previous studies using otoacoustic emissions. Successful classification of single-trial data could additionally have a significant impact on future closed-loop CI developments that incorporate real-time optimization of CI parameters based on the current mental state of the user.SIGNIFICANCE STATEMENT The efferent auditory system in principle allows top-down modulation of auditory nerve activity; however, evidence for this is lacking in humans. Using cochlear recordings in participants performing an audiovisual attention task, we show that ongoing auditory nerve activity in the silent cue-target period is directly modulated by selective attention. Specifically, ongoing auditory nerve activity is enhanced within the theta range when attending upcoming auditory input. Furthermore, over a broader frequency range, the attended modality can be decoded from single-trial data. Demonstrating this direct top-down influence on auditory nerve activity substantially extends previous works that focus on outer hair cell activity. Generally, our work could promote the use of standard cochlear implant electrodes to study cognitive neuroscientific questions.

Standard cochlear implants as electrochemical sensors: Intracochlear oxygen measurements in vivo

Cochlear implants are the most successful neural prostheses worldwide and routinely restore sensorineural hearing loss by direct electrical stimulation of the auditory nerve. Enhancing this standard implant by chemical sensor functionality opens up new possibilities, ranging from access to the biochemical microenvironment of the implanted electrode array to the long-term study of the electrode status. We developed an electrochemical method to turn the platinum stimulation microelectrodes of cochlear implants into electrochemical sensors. The electrodes showed excellent and stable chemical sensor properties, as demonstrated by in vitro characterizations with combined amperometric and active potentiometric dissolved oxygen and hydrogen peroxide measurements. Linear, stable and highly reproducible sensor responses within the relevant concentration ranges with negligible offset were shown. This approach was successfully applied in vivo in an animal model. Intracochlear oxygen dynamics in rats upon breathing pure oxygen were reproducibly and precisely measured in real-time from the perilymph. At the same time, correct implant placement and its functionality was verified by measurements of electrically evoked auditory brainstem responses with clearly distinguishable peaks. Acute measurements indicated no adverse influence of electrical stimulation on electrochemical measurements and vice versa. Our work is ground-breaking towards advanced implant functionality, future implant lifetime monitoring, and implant-life-long in situ investigation of electrode degradation in cochlear implant patients.

Reduced Spread of Electric Field After Surgical Removal of Intracochlear Schwannoma and Cochlear Implantation.

The primary aim of the study was to explore whether reduced spread of electrical field is observed after partial or subtotal cochleoectomy and cochlear implantation compared with standard cochlear implantation. Secondarily, the influence on speech perception was explored comparing both groups. Nonconcurrent cohort study. Monocentric study at a tertiary referral center. Twenty adult cochlear implant (CI) users after tumor resection with cochleoectomy of varying extent and 20 electrode-matched CI users with standard electrode insertion. Partial and subtotal cochleoectomy for tumor removal and CI. Trans-impedance, electrically evoked compound action potentials, and word recognition were measured. Relative impedance was computed as a function of distance between the stimulation and recording electrode. Trans-impedance was smaller and more homogeneous in patients with partial or subtotal cochleoectomy than in the control group. In the tumor group, the mean relative impedance decreased to 0.20 (standard deviation [SD] = 0.03) at a distance of 1 electrode and to 0.25 (SD = 0.04) in the control group. After excluding seven patients with a second tumor in the internal auditory canal or cerebellopontine angle, with transmodiolar tumors, after near total cochleoectomy, or only extended cochleostomy, word recognition was 61% (SD = 19%) at 3 months and 75% (SD = 19%) at 12 months after activation of the audio processor in the tumor group. At 12 months, it was significantly (p < 0.05) better than in the control group (3 mo: 45%, SD = 25%; 12 mo: 53%, SD = 26%). A smaller trans-impedance is associated with a better word recognition. We conclude that the surgical technique used for CI surgery after subtotal cochleoectomy reduces the spread of the electric field and overcomes the potential drawbacks in structure preservation associated with that technique.

Prevalence of potential candidates for electric-acoustic stimulation implant in a hearing-impaired population

ObjectiveTo estimate the prevalence of potential electric-acoustic stimulation (EAS) implant candidates in a hearing-impaired population through a review of auditory examinations. MethodsIn total, 7356 patients underwent audiometric examination in our department between 2011 and 2014. The prevalence of patients meeting the audiometric criteria for EAS and standard cochlear implant (CI) was assessed. ResultsThe percentage of EAS implant candidates meeting the pure-tone audiometric criteria was 0.71% (n=34) among the hearing-impaired individuals (n=4758) examined in our department, whereas 2.52% (n=120) met the criteria for standard CI. Among the 34 EAS implant candidates, 2 individuals (5.83%) received EAS implant surgery after approval of the EAS device in Japan. ConclusionsThere was a lower prevalence of EAS implant candidates than standard CI candidates. Nevertheless, healthcare professionals should carefully examine the audiograms of patients with high frequency hearing loss with regard to meeting the indication criteria for EAS implant. This will enable patients to gain access to adequate information relating to further examinations and treatment options.

Does cochlear implantation influence postural stability in patients with hearing loss?

BackgroundCochlear implantation (CI) procedure carries the potential risk for vestibular system insult or stimulation with resultant dysfunction due to its proximity to the cochlea. The vestibular system plays an essential role in crucial tasks such as postural control, gaze stabilization and spatial orientation. Research questionHow does standard cochlear implantation influence postural stability in patients with hearing loss? MethodsThe study included 21 individuals (age 51 ± 18 years) qualified to undergo CI due to severe or profound hearing loss. Participants were qualified for both groups by a physician based on an interview, an otoneurological examination and vestibular tests. The first group included patients without vestibular dysfunction, whereas the other group consisted of persons with vestibular dysfunction. The research methodology included medical examinations, anthropometric measurements and stabilometry on the Biodex Balance System SD (BBS) platform. The examinations were carried out twice, i.e. prior to and 3 months post implantation. The recorded data was compared between the first and the second examination using a non-parametric Wilcoxon test. The analysis of variance (ANOVA) and Tukey’s post-hoc HSD unequal sample sizes were performed for patients with and without vestibular dysfunction. Results and SignificanceStudy showed that 52.4% of the participants obtained results within the norm, while 47.6% scored below it. The comparison of stability indices of the examined individuals, with and without vestibular dysfunction, did not reveal statistically significant differences. The only difference was the anterior-posterior stability index assessed in static conditions. Three months after the implantation, no changes in the majority of indices were noted, with the exception of anterior-posterior stability index, which improved following the implantation. CI does not affect postural stability changes in the study participants.

Prevalence of Extracochlear Electrodes: Computerized Tomography Scans, Cochlear Implant Maps, and Operative Reports.

To quantify and compare the number of cochlear implant (CI) electrodes found to be extracochlear on postoperative computerized tomography (CT) scans, the number of basal electrodes deactivated during standard CI mapping (without knowledge of the postoperative CT scan), and the extent of electrode insertion noted by the surgeon. Retrospective. Academic Medical Center. Two hundred sixty-two patients underwent standard cochlear implantation and postoperative temporal bone CT scanning. Scans were analyzed to determine the number of extracochlear electrodes. Standard CI programming had been completed without knowledge of the extracochlear electrodes identified on the CT. These standard CI maps were reviewed to record the number of deactivated basal electrodes. Lastly, each operative report was reviewed to record the extent of reported electrode insertion. 13.4% (n = 35) of CIs were found to have at least one electrode outside of the cochlea on the CT scan. Review of CI mapping indicated that audiologists had deactivated extracochlear electrodes in 60% (21) of these cases. Review of operative reports revealed that surgeons correctly indicated the number of extracochlear electrodes in 6% (2) of these cases. Extracochlear electrodes were correctly identified audiologically in 60% of cases and in surgical reports in 6% of cases; however, it is possible that at least a portion of these cases involved postoperative electrode migration. Given these findings, postoperative CT scans can provide information regarding basal electrode location, which could help improve programming accuracy, associated frequency allocation, and audibility with appropriate deactivation of extracochlear electrodes.

Mondini deformity implanted with minimal incision

Mondini deformity accounts for majority of cochlear malformations. These children can be given a near-normal lifestyle by performing cochlear implant (CI) surgery. The results of standard incision cochlear implantation (SICI) in these children are very encouraging. However, there are very few centers in world which offer the minimal incision cochlear implantation (MICI) in these patients. We report a case of 2-year-old child suffering from Mondini deformity who underwent CI with MICI. MICI reduces the impact of surgery drastically in these children as it can be performed without shaving of hairs with a 2-cm incision. The complication rate of MICI is comparable to SICI. Apart from better cosmesis, another advantage is early switch on of the device. We are of the opinion that MICI is safe and can be successfully performed in cases of Mondini deformity without any fear.

Treating the Signature Injury

Treating the Signature Injury

Minimal access and standard cochlear implantation: A comparative study

ObjectiveTo compare the operative times and complications between patients who underwent minimal access cochlear implantation and standard technique cochlear implantation. MethodsPatients who underwent unilateral cochlear implantation by a single surgeon from 2001 to 2010. The minimal access technique of an approximately 2.5–3cm post-auricular incision with creation of subperiosteal pocket for the device was compared to the longer standard “S” incision into the scalp (∼8–10cm) with bone well creation and suture fixation. Outcomes include operative times and complications. ResultsThere were 122 unilateral implants, 73 (59.8%) in the minimal access group and 49 (40.2%) in the standard group. Mean total time in the operating room was lower in the minimal access group compared to the standard group (200±31 vs. 255±49min, p<.0001) as well as mean operative time (149.5±28 vs. 200±45min, p<.0001 respectively).There were 17 complications in the entire cohort with 8 and 9 complications in the minimal and standard groups respectively. Of the 17 complications, 12 were surgical technique-specific. Although it appeared that there were higher rates of major, technique-specific, and overall complications in the standard access group, these differences did not reach statistical significance. ConclusionsPatients undergoing minimal access cochlear implantation require shorter operative times when compared to the standard access cochlear implantation. In addition, low complication rates are observed for major, technique-specific, and overall complications. Minimal access cochlear implantation may be considered an equivalent and potentially superior technique.

The Evaluation of Patients with Partial Deafness by Transiently Evoked Otoacoustic Emissions

Otoacoustic emissions (OAEs) are well established in clinical practice and are a valuable tool in basic research (Probst et al., 1991). The most commonly used OAEs are click-evoked OAEs (CEOAEs) and distortion product OAEs (DPOAEs), which are evoked by two tonal stimuli. OAEs are believed to be good predictors of hearing status, particularly in the 1–4 kHz range. However, while DPOAEs perform more satisfactorily at higher frequencies, CEOAEs are better indicators of cochlear function at lower frequencies. OAEs are known to be frequency-specific. In most cases, OAEs do not occur when hearing loss is greater than 35 dB HL. However, if hearing is preserved at a certain frequency, there is then the possibility of recording OAEs at this specific frequency (Kemp et al., 1986). It is the basal region of the cochlea that is most prone to damage. That is reflected in OAEs that tend to have a lower amplitude or even disappear first at the higher frequencies when hearing loss is present. Transiently evoked OAEs can also be elicited by so-called ‘tone bursts’, which are short stimuli centred at a certain frequency. Several studies have shown that the spectral content of a sum of tone burst-evoked OAEs (TBOAEs) centred in the 1–4 kHz corresponds to CEOAE. It is nevertheless the case that, for tone bursts, the same level of stimulus as the equivalent click gives a higher level of OAE. Therefore those stimuli can give an advantage over standard clicks in some difficult cases. The OAE is absent in a majority of patients who undergo standard cochlear implantation. However, as it will be shown below, by using tone bursts as a stimuli it is possible to measure OAEs in some of the partial deafness subjects.

Hearing Preservation in Patients With a Cochlear Implant

Hearing Preservation in Patients With a Cochlear Implant

Standard Cochlear Implantation of Adults With Residual Low-Frequency Hearing

This study compared preoperative and postoperative cochlear implant benefit in subjects with steeply sloping high-frequency hearing losses (HLs) who were implanted with standard long cochlear implant electrodes to: 1) determine the effect of etiology, 2) compare outcomes in studies exploring the use of combined electrical and acoustic stimulation, and 3) compare outcomes in patients implanted using standard criteria. Retrospective case review. Tertiary referral center. Nine adults with steeply sloping high-frequency congenital (n=2) or acquired (n=7) bilateral sensorineural HL. All pure-tone audiograms fit the criteria for trials of a short electrode aimed at preserving low-frequency acoustic hearing. Subjects received full insertion of a standard cochlear implant long electrode in the poorer ear. Preoperative versus postoperative audiograms, word and sentence recognition in quiet and noise. Patients with progressive acquired HLs experienced significantly improved speech understanding in quiet and in noise with the cochlear implant, especially when combined with hearing aid use in the contralateral ear. Patients with congenital HLs experienced little or no improvement in the implanted ear when tested with the implant alone, but achieved some benefit when the implant was combined with a hearing aid in the nonimplanted ear. Based on this small sample, patients with acquired steeply sloping high-frequency HLs obtain significant benefit from cochlear implantation with standard long electrodes. In progressive losses, full insertion of a long electrode would be preferable to a short electrode because acoustic hearing may diminish over time. In contrast, patients with congenital losses may not benefit from long electrodes, and might be better served by implanting a short electrode, thereby allowing use of low-frequency acoustic stimulation.

Modifications of standard cochlear implantation techniques for children under 18 months of age

Cochlear implantation is being performed in increasingly younger children. We present a retrospective cohort of 19 patients with 23 ears implanted under 18 months of age. The mean age at implantation was 11.9 months, with the youngest being 6.8 months. The facial recess was narrow in nine ears (39%), including all premature infants. An inferiorly located stapedius tendon was sectioned in seven ears (30%) to facilitate round window access. Countersinking of the receiver-stimulator required dural exposure in 22 ears (96%). The receiver-stimulator was secured with sutures in 15 ears (65%) and within a tight pocket in eight ears (35%). Tympanostomy tubes were placed in 10 ears (43%). Cochlear implantation in very young children frequently necessitates modified surgical techniques. Copyright © 2006 John Wiley & Sons, Ltd.

Acoustic plus Electric Speech Processing: Preliminary Results of a Multicenter Clinical Trial of the Iowa/Nucleus Hybrid Implant

Aim: This communication details the latest preliminary results from an ongoing multicenter single-subject design clinical trial of the Iowa/Nucleus Hybrid 10-mm cochlear implant. Selection criteria, surgical strategies used for hearing preservation, and the benefits of preserved residual low-frequency hearing, improved word understanding in noise, and music appreciation are described. Patients and Methods: The device has been implanted in 48 individuals with residual low-frequency hearing. Results:Hearing preservation has been accomplished in 46/48 subjects. Acoustic speech perception has also been preserved. Combined acoustic plus electric speech processing has enabled most of this group of volunteers to gain improved word understanding as compared to their preoperative hearing with bilateral hearing aids. A subset of subjects with 12 months or more experience demonstrates CNC word understanding continues to improve more than 24 months after implantation. Improved word understanding in noise is also a benefit of acoustic plus electric speech processing. Conclusions:The improvement of speech in noise and melody recognition is linked to the ability to distinguish fine pitch differences as the result of preserved residual low-frequency acoustic hearing. Both of these measures are very important in real life to the hearing impaired. Preservation of residual low-frequency hearing should be considered when expanding candidate selection criteria for standard cochlear implants.

Complication rate of minimally invasive cochlear implantation

To assess the complication rate of minimally invasive cochlear implantation (MICI). Data for this study were obtained via a retrospective analysis of records at the Ear Medical Group, San Antonio, TX, after IRB approval at the University of Texas Health Science Center at San Antonio. The surgical complications of MICI were recorded in a spreadsheet format; 176 patients were included in the study. A total of 22 (12.5%) complications were noted in the study. There were 0 life-threatening, 7 major, and 15 minor complications. Of the 7 major complications, 3 were device failures, 2 developed delayed mastoiditis, 1 required receiver/stimulator repositioning, and 1 involved facial paralysis. MICI is as safe as standard cochlear implantation (SCI) and affords with it other benefits. Eliminating the scalp flap avoids devascularization and minimizes the opportunity of flap infection or necrosis. Complications not related to the flap are similar to SCI. C-4.

Modifications of standard cochlear implantation techniques for children under 18 months of age

Modifications of standard cochlear implantation techniques for children under 18 months of age

Investigations on the clinical significance of cochlear implantation in the modiolus

Problem: The purpose of this study was to disclose the possibilities for implantation of an electrode in the modiolus for stimulation of auditory nerve in cases of severe hearing loss. Methods: Our methods consisted of the dissection of human temporal bones, and histological investigation of modiolar structure before and after the insertion of an electrode. Results: Ten dissections of human temporal bones were carried out. A plastic copy of an electrode was implanted in the modiolus. Histological investigations were made in order to clarify the anatomic variations of modiolus and the eventual destructive changes that may occur during the implantation. Conclusion: It was found that the best surgical approach to the modiolus is through middle cranial fossa. The cupula of the cochlea is located medially and anteriorly to ganglion geniculi. The greater petrosal nerve serves as a landmark. The nerve is elevated, the bone is drilled from its sulcus to the cupula cochleae, which is found at about 2 mm depth. After entering the cupula, the top of the modiolus is visualized. A canal should be made by a special probe, which should be introduced without any pressure along canalis longitudinalis modioli, due to the very soft modiolar tissue. Invasion of the electrode into the first 2 mm of internal auditory canal does not harm the hearing nerve fibers, which are still not fused to form the auditory nerve. Histological studies did not show injury of modiolar structures. Significance: We believe that the implantation of an electrode in the modiolus could be an alternative to standard cochlear implantation and may even be preferable in cases with chronic middle ear inflammation and cochlear ossification. Support: None reported.