Auditory Brainstem Implant Users Research Articles

Subjective outcomes of auditory brainstem implantation.

To assess the long-term subjective benefits of auditory brainstem implants (ABIs) and investigate the extent to which ABI users perceive it to be a useful device. Using the Manchester database, all 31 living patients registered as ABI users were identified and sent the ABI performance questionnaire. Data regarding daily duration of use, auditory fatigue, ability to differentiate between speech and environmental sounds, and subjective usefulness of the ABI in different listening conditions were collected. Patients were asked to rate the usefulness of the device in various settings on a scale of 1 (not useful) to 6 (very useful). The mean age at implantation was 33 years (13-73 yr), and the mean follow-up period was 6 years (1.5-15 yr). Between March 1994 and September 2009, 57 patients underwent ABI insertion. A total of 26 patients were not eligible for inclusion in the study (19 nonusers, 5 deceased, and 2 sleepers). Of the 31 eligible patients identified as ABI users, 23 returned the questionnaire, 1 was excluded as the questionnaire had been completed on his or her behalf, giving a net response rate of 71%. Mean duration of usage per day was 12.62 hours (range, 8-16 h). Seventy-one percent of the patients turned the processor off at one or more points during the day. Differentiation between speech and environment was achieved in 95%, and 70% were able to differentiate between gender and adult and pediatric voices. The ABI was perceived as most beneficial when dealing with a familiar voice in a quiet place, with a median usefulness score of 4, rising to 5 when used in conjunction with lip reading. The ABI was least useful when dealing with an unfamiliar voice in a loud place, with a mean score of 1, rising to 2 when used in conjunction with lip reading. In all environments, combining the ABI with lip reading served to increase usefulness ratings by at least 1 point. This study demonstrates that ABI users make use of their device for at least 12 hours per day on average and obtain considerable subjective benefit in speech discrimination when using the device with familiar speakers in a quiet environment. Benefit is less significant in noise and with an unfamiliar speaker. Lip reading enhances subjective benefit by at least 1 point, and lip reading training may have a role to play in maximizing subjective benefit.

Inserting the speech signal above the cochlea: How can this work?

Although cochlear implants (CIs) have successfully restoring hearing to many deaf people, there remains a subgroup who cannot benefit from them due to malformation of the cochlea or damage to the cochlear nerve. Auditory brainstem implants (ABIs) and auditory midbrain implants (AMIs) aim to restore hearing to this group. ABIs stimulate the surface of the cochlear nucleus (CN). Despite some ABI users gaining benefit similar to a CI, the majority achieve poor speech understanding with the device alone. The reasons for poor outcomes are not fully understood but include tumor damage to particular cells in the cochlear nucleus, surgical approach, and placement of the electrodes. One factor in poor outcome is the difficulty of stimulating specific tonotopic planes within the CN. This factor and tumor damage to the CN were reasons for the development of the AMI, which directly stimulates the tonotopic layers of the inferior colliculus (IC) using a shank electrode. Psychophysics and physiological studies have thr...

Processing of speech temporal and spectral information by users of auditory brainstem implants and cochlear implants.

Auditory brainstem implants (ABI) use the same processing strategy as was developed for cochlear implants (CI). However, the cochlear nucleus (CN), the stimulation site of ABIs, is anatomically and physiologically more complex than the auditory nerve and consists of neurons with differing roles in auditory processing. The aim of this study was to evaluate the hypotheses that ABI users are less able than CI users to access speech spectro-temporal information delivered by the existing strategies and that the sites stimulated by different locations of CI and ABI electrode arrays differ in encoding of temporal patterns in the stimulation. Six CI users and four ABI users of Nucleus implants with ACE processing strategy participated in this study. Closed-set perception of aCa syllables (16 consonants) and bVd words (11 vowels) was evaluated via experimental processing strategies that activated one, two, or four of the electrodes of the array in a CIS manner as well as subjects' clinical strategies. Three single-channel strategies presented the overall temporal envelope variations of the signal on a single-implant electrode located at the high-, medium-, and low-frequency regions of the array. Implantees' ability to discriminate within electrode temporal patterns of stimulation for phoneme perception and their ability to make use of spectral information presented by increased number of active electrodes were assessed in the single- and multiple-channel strategies, respectively. Overall percentages and information transmission of phonetic features were obtained for each experimental program. Phoneme perception performance of three ABI users was within the range of CI users in most of the experimental strategies and improved as the number of active electrodes increased. One ABI user performed close to chance with all the single and multiple electrode strategies. There was no significant difference between apical, basal, and middle CI electrodes in transmitting speech temporal information, except a trend that the voicing feature was the least transmitted by the basal electrode. A similar electrode-location pattern could be observed in most ABI subjects. Although the number of tested ABI subjects was small, their wide range of phoneme perception performance was consistent with previous reports of overall speech perception in ABI patients. The better-performing ABI user participants had access to speech temporal and spectral information that was comparable to that of average CI user. The poor-performing ABI user did not have access to within-channel speech temporal information and did not benefit from an increased number of spectral channels. The within-subject variability between different ABI electrodes was less than the variability across users in transmission of speech temporal information. The difference in the performance of ABI users could be related to the location of their electrode array on the CN, anatomy, and physiology of their CN or the damage to their auditory brainstem due to tumor or surgery.

Methods and Preliminary Outcomes of Pediatric Auditory Brainstem Implantation

The objective was to provide information about methods used and preliminary outcomes for pediatric ABI (auditory brainstem implant). An analysis of outcome was performed in children who received an ABI. Twelve children received a MED-EL ABI system. Progress in audition and language was monitored through parental reports, questionnaires, profiles, and closed-set tests. The median number of active electrodes was 9 of 12. Seven of 12 users consistently respond to sound, and 5 of 12 do not. Highest performers can recognize words in small sets and have begun to use some words. Auditory brainstem implants appear to be beneficial for some pediatric patients who cannot benefit from traditional cochlear implant surgery. Benefits in the short-term can be recognition of environmental sounds, recognition of some words and very commonly used phrases, and the beginning use of words. Although some of our ABI users demonstrate no response to sound, they do want to wear their sound processors all waking hours. The cause of lack of response may be related to the second intervention, which might have led to displacement of the electrode array, or presence of additional handicaps or syndromes. However, the results are less than optimal. The relatively short postoperative follow-up duration is a considered weakness of this study.

Encoding of the amplitude modulation of pulsatile electrical stimulation in the feline cochlear nucleus by neurons in the inferior colliculus; effects of stimulus pulse rate

Objectives. Persons without a functional auditory nerve cannot benefit from cochlear implants, but some hearing can be restored by an auditory brainstem implant (ABI) with stimulating electrodes implanted on the surface of the cochlear nucleus (CN). Most users benefit from their ABI, but speech recognition tends to be poorer than for users of cochlear implants. Psychophysical studies suggest that poor modulation detection may contribute to the limited performance of ABI users. In a cat model, we determined how the pulse rate of the electrical stimulus applied within or on the CN affects temporal and rate encoding of amplitude modulation (AM) by neurons in the central nucleus of the inferior colliculus (ICC). Approach. Stimulating microelectrodes were implanted chronically in and on the cats' CN, and multi-site recording microelectrodes were implanted chronically into the ICC. Encoding of AM pulse trains by neurons in the ICC was characterized as vector strength (VS), the synchrony of neural activity with the AM, and as the mean rate of neuronal action potentials (neuronal spike rate (NSR)). Main results. For intranuclear microstimulation, encoding of AM as VS was up to 3 dB greater when stimulus pulse rate was increased from 250 to 500 pps, but only for neuronal units with low best acoustic frequencies, and when the electrical stimulation was modulated at low frequencies (10–20 Hz). For stimulation on the surface of the CN, VS was similar at 250 and 500 pps, and the dynamic range of the VS was reduced for pulse rates greater than 250 pps. Modulation depth was encoded strongly as VS when the maximum stimulus amplitude was held constant across a range of modulation depth. This ‘constant maximum’ protocol allows enhancement of modulation depth while preserving overall dynamic range. However, modulation depth was not encoded as strongly as NSR. Significance. The findings have implications for improved sound processors for present and future ABIs. The performance of ABIs may benefit from using pulse rates greater than those presently used in most ABIs, and by sound processing strategies that enhance the modulation depth of the electrical stimulus while preserving dynamic range.

An in vivo investigation of inferior colliculus single neuron responses to cochlear nucleus pulse train stimulation

The auditory brain stem implant (ABI) is being used clinically to restore hearing to patients unable to benefit from a cochlear implant (CI). Speech perception outcomes for ABI users are typically poor compared with most CI users. The ABI is implanted either on the surface of or penetrating through the cochlear nucleus in the auditory brain stem and uses stimulation strategies developed for auditory nerve stimulation with a CI. Although the stimulus rate may affect speech perception outcomes with current stimulation strategies, no studies have systematically investigated the effect of stimulus rate electrophysiologically or clinically. We therefore investigated rate response properties and temporal response properties of single inferior colliculus (IC) neurons from penetrating ABI stimulation using stimulus rates ranging from 100 to 1,600 pulses/s in the rat. We found that the stimulus rate affected the proportion of response types, thresholds, and dynamic ranges of IC activation. The stimulus rate was also found to affect the temporal properties of IC responses, with higher rates providing more temporally similar responses to acoustic stimulation. Suppression of neural firing and inhibition in IC neurons was also found, with response properties varying with the stimulus rate. This study demonstrated that changes in the ABI stimulus rate results in significant differences in IC neuron response properties. Due to electrophysiological differences, the stimulus rate may also change perceptual properties. We suggest that clinical evaluation of the ABI stimulus rate should be performed.

Auditory Brainstem Implant in Neurofibromatosis Type 2 and Non-Neurofibromatosis Type 2 Patients

To evaluate the auditory brainstem implant (ABI) performances in neurofibromatosis type 2 (NF2) and non-NF2 patients. Retrospective cohort study. Tertiary referral center. Between 1996 and 2006, 31 adult patients (mean age, 41 yr; range, 17-65 yr) were implanted with a 21-electrode Nucleus device (Cochlear Inc., Lane Cove, Australia). The population comprised 23 NF2, 3 postmeningitis bilateral ossified cochleas, 3 solitary vestibular schwannomas on the only hearing ear, 1 inner ear malformation, and 1 bilateral cochlear destruction by otosclerosis. Auditory brainstem implant was placed through a translabyrinthine or a retrosigmoid approach. Auditory brainstem implant was evaluated by open-set words and sentences in sound, vision, and sound-plus-vision modes. In NF2 patients, 16 (70%) were daily users of their implants. In these patients, the open-set dissyllabic word recognition was 36 +/- 6.0 % for vision-only mode, 33 +/- 6.5 % for sound-only mode, and 65 +/- 8.0 % in vision-plus-sound mode with a high interindividual variation. Negative prognostic factors were long duration of total hearing loss (>10 yr), low number of active electrodes (<10), and local complications (meningitis, hematoma). Six non-NF2 patients (75%) were daily ABI users. The performances of patients with ossified cochleas were similar to best NF2 cases. A clear benefit of ABI could be evidenced in NF2 patients, especially in case of small tumor and short duration of hearing loss. Auditory brainstem implant may also be indicated in patients with bilateral profound hearing loss and a predictable failure of cochlear implantation.

Optimizing the Clinical Fit of Auditory Brain Stem Implants

To develop and implement a new audiological fitting procedure for auditory brain stem implants (ABIs), based on an efficient algorithm, and to compare it with two procedures presently used in clinical practice. First, the different procedures were compared by using computer models and simulations with normal-hearing subjects (N = 4). This allows for an analysis of the accuracy of the procedures in a way that is not possible when testing ABI users. The root-mean-square error between the order estimated by the procedure and the true order was calculated. In addition, ABI users (N = 2) were tested with the new procedure to see if it could be successfully applied in clinic. The degree of variability of their results across runs and sessions was analyzed. The tests of the normal-hearing subjects showed that our proposed procedure required significantly fewer trials (22 on average) than procedures presently used in clinic (with 76 and 234 trials on average for the two other procedures tested) to produce the same degree of accuracy. Computer modeling also demonstrated this advantage. Additional testing showed this advantage was maintained under a variety of conditions relevant to the clinic. The two patients tested were able to use this procedure with success, even though they were poor at discriminating the pitch of electrodes. The patients showed results consistent with having about 4 to 5 discriminable groups of electrodes with the 12 to 14 electrodes tested. The proposed procedure requires fewer trials to produce a clinically useful result and is well tolerated in the clinic. An additional advantage is that it allows testing to be broken down into several "blocks," each containing a small number of trials. If the variability between blocks is small, information can be combined across blocks to increase the accuracy of the result. If the variability is large, perhaps between blocks on different days, this may reflect a significant change in the percepts generated by the implant, and signal to the clinician that a significant alteration in the fitting is required. We recommend its use in ABI user fitting and in cochlear implant fitting when pitch ranking is problematic.