Steven R. Otto

Cochlear implants : histopathologic findings related to performance in 16 human temporal bones

This paper presents results of a histologic study of 16 temporal bones with cochlear implants from 13 subjects. Damage caused by electrode insertion in the basal turn of the cochlea was evaluated. Dendrite and spiral ganglion cell populations were compared to clinical performance scores to determine structures necessary for stimulation and the minimum number needed for electrical stimulation. Results show that damage from insertion of long electrodes was located mainly at the most anterior part of the basal turn; that despite total degeneration of dendrites in the area near the electrode, some spiral ganglion cells remained; and that spiral ganglion cells or possibly axons are the stimulated structures and that fewer of them than previously thought are necessary to achieve a hearing sensation from electrical stimulation.

Auditory brainstem implants

SummaryThe development of cochlear implantation has allowed the majority of patients deafened after the development of language to regain significant auditory benefit. In a subset of patients, however, loss of hearing results from destruction of the cochlear nerves, rendering cochlear implantation ineffective. The most common cause of bilateral destruction of the cochlear nerves is neurofibromatosis type 2 (NF2). The hallmark of this genetic disorder is the development of bilateral acoustic neuromas, the growth or removal of which causes deafness in most patients. Patients with NF2 may benefit from direct stimulation of the cochlear nucleus. We describe the development, use, and results of the auditory brainstem implant (ABI), which is typically implanted via craniotomy at the time of tumor removal. Most patients with the implant have good appreciation of environmental sounds, but obtain more modest benefit with regard to speech perception. The majority of patients make use of the implant to facilitate lip reading; some can, to varying degrees, comprehend speech directly. We discuss future directions in central implants for hearing, including the penetrating ABI, the use of ABI in nontumor patients, and the auditory midbrain implant.

Psychophysical measures from electrical stimulation of the human cochlear nucleus

Auditory performance on basic psychophysical tasks was measured in ten deaf patients with electrodes positioned near their cochlear nucleus. The device is called the auditory brainstem implant (ABI). Electrodes were placed during surgery to remove an acoustic neuroma, which results in the removal of the VIII nerve and, thus deafness. In patients who received auditory sensation from electrical stimulation we measured auditory performance on standard psychophysical tasks: thresholds, loudness growth, intensity discrimination, temporal integration, temporal modulation detection, gap detection, and forward masking. Plots of threshold as a function of frequency or biphasic pulse duration were markedly different from those of patients with cochlear implants. The difference in threshold functions is probably partly due to the biophysical difference in the neural elements stimulated. Another possibility is that part of the difference is due to the highly abnormal spatial pattern of activation in the cochlear nucleus from electrical stimulation, which prevents normal spatial integration of activity. The usable range of electrical amplitudes above threshold is comparable with that of cochlear implants, typically 10-15 dB. Little temporal integration occurs over a range of stimulus durations from 2-1000 ms. When compared at equivalent loudness levels, gap detection thresholds are similar to, or a bit longer than, gap thresholds in normal-hearing listeners and cochlear implant patients. Forward masking recovery functions are similar to those of normal listeners and cochlear implant patients. Patients ability to detect amplitude modulation as a function of modulation frequency is similar to that of cochlear implant patients and normal listeners. Thus, direct electrical stimulation of the brainstem produces temporal resolution that does not significantly differ from that of normal listeners when compared in equivalent amplitude units. This implies that the limiting factors for these tasks are more centrally located, and not directly related to threshold mechanisms. Thus, a properly designed speech processor could preserve the important temporal features of speech for these patients.

Audiologic outcomes with the penetrating electrode auditory brainstem implant.

Objective: The penetrating electrode auditory brainstem implant (PABI) is an extension of auditory brainstem implant (ABI) technology originally developed for individuals deafened by neurofibromatosis type 2. Whereas the conventional ABI uses surface electrodes on the cochlear nuclei, the PABI uses 8 or 10 penetrating microelectrodes in conjunction with a separate array of 10 or 12 surface electrodes. The goals of the PABI were to use microstimulation to reduce threshold current levels, increase the range of pitch percepts, and improve electrode selectivity and speech recognition. Patients and Protocol: In a prospective clinical trial, 10 individuals, all with neurofibromatosis type 2, received a PABI after vestibular schwannoma removal via a translabyrinthine approach. All study participants met strict requirements for informed consent as part of a Food and Drug Administration clinical trial. Approximately 8 weeks after implantation, PABI devices were activated and tested at our tertiary clinical and research facility. Mean follow-up time was 33.8 months. Study Design: Using a single-subject design, we measured thresholds and dynamic ranges, electrode-specific pitch percepts, and speech perception performance at regular intervals. Results: Penetrating electrodes produced auditory thresholds at substantially lower charge levels than surface electrodes, a wide range of electrode-specific pitch sensations, and minimal cross-electrode interference and could be used in speech maps either alone or in combination with surface electrodes. However, less than 25% of penetrating electrodes resulted in auditory sensations, whereas more than 60% of surface electrodes were effective. Even after more than 3 years of experience, patients using penetrating electrodes did not achieve improved speech recognition compared with those using surface electrode ABIs. In patients with usable penetrating electrodes, City University of New York Sentence Test scores with sound and visual information were 61.6% in the PABI group and 64.7% in a surface ABI cohort (p = not significant). Conclusion: The PABI met the goals of lower threshold, increased pitch range, and high selectivity, but these properties did not result in improved speech recognition.

Use of a Multichannel Auditory Brainstem Implant for Neurofibromatosis Type 2

Neurofibromatosis type 2 (NF 2) typically results in deafness due to disruption of the cochlear nerves, making peripheral devices such as cochlear implants ineffective. Auditory brainstem implants (ABIs), for direct electrical stimulation of the cochlear nucleus, have been used to provide auditory stimulation in this group of patients. Currently, 141 patients have been implanted in our institution, most recently using an advanced multichannel device. We report results of a recent series of 86 patients who received ABIs. Of this group, 60 had successful implantation, recovered from surgery, responded successfully to stimulation and underwent a full course of device programming and audiologic testing. This group had significant improvement in scores on several audiologic tests compared to baseline. When used to augment lip reading, improvement was also seen. The degree of improvement varied considerably among patients. ABI is a useful device for deaf patients with NF 2. As measured by audiologic testing, many patients receive substantial benefit with regard to sound and speech comprehension.

Auditory Brain Stem Implant: Effect of Tumor Size and Preoperative Hearing Level on Function

The auditory brain stem implant is an investigational device designed to provide hearing sensations to patients without functioning auditory nerves. We analyzed results from 17 implants in 15 patients to determine if tumor size or preoperative hearing level might be related to proper device function. We found no significant correlation between preoperative hearing level or tumor size and device function. We also found no significant correlation between preoperative hearing level and tumor size in these 15 patients.

Histopathological analysis of a 15-year user of an auditory brainstem implant.

Auditory brainstem implants (ABIs) can provide highly beneficial hearing sensations to individuals deafened by bilateral vestibular schwannomas (neurofibromatosis type 2). Relatively little is known about the status of stimulated neurons after long‐term ABI use. Direct examination of the cochlear nuclear complex (CN) of one 5‐year ABI user indicated no deleterious effect. Recently, we examined the brainstem of a patient who used his ABI daily for 15 years with excellent performance. There was good preservation of CN cell size, morphology, and packing density, a very favorable sign considering that a number of infants are now receiving ABIs.

Brainstem auditory implants

Abstract Neurofibromatosis type 2 (NF 2) typically results in deafness due to disruption of the cochlear nerves, making peripheral devices such as cochlear implants ineffective. Auditory brainstem implants (ABIs), for direct electrical stimulation of the cochlear nucleus, have been used to provide auditory stimulation in this group of patients. Currently, an advanced multichannel device is utilized, with direct stimulation of the brainstem surface. Patients undergoing ABI have significant improvement in scores on several audiologic tests over baseline. When used to augment lip reading, improvement is also seen. The degree of improvement varies considerably among patients. ABI is a useful device for use by deaf patients with NF 2. As measured by audiologic testing, many patients receive substantial benefit with regard to sound and speech comprehension.