Tinnitus suppression by electric stimulation of the auditory nerve.

Electric stimulation of the auditory nerve via a cochlear implant (CI) has been observed to suppress tinnitus, but parameters of an effective electric stimulus remain unexplored. Here we used CI research processors to systematically vary pulse rate, electrode place, and current amplitude of electric stimuli, and measure their effects on tinnitus loudness and stimulus loudness as a function of stimulus duration. Thirteen tinnitus subjects who used CIs were tested, with nine (70%) being "Responders" who achieved greater than 30% tinnitus loudness reduction in response to at least one stimulation condition and the remaining four (30%) being "Non-Responders" who had less than 30% tinnitus loudness reduction in response to any stimulus condition tested. Despite large individual variability, several interesting observations were made between stimulation parameters, tinnitus characteristics, and tinnitus suppression. If a subject's tinnitus was suppressed by one stimulus, then it was more likely to be suppressed by another stimulus. If the tinnitus contained a "pulsating" component, then it would be more likely suppressed by a given combination of stimulus parameters than tinnitus without these components. There was also a disassociation between the subjects' clinical speech processor and our research processor in terms of their effectiveness in tinnitus suppression. Finally, an interesting dichotomy was observed between loudness adaptation to electric stimuli and their effects on tinnitus loudness, with the Responders exhibiting higher degrees of loudness adaptation than the Non-Responders. Although the mechanisms underlying these observations remain to be resolved, their clinical implications are clear. When using a CI to manage tinnitus, the clinical processor that is optimized for speech perception needs to be customized for optimal tinnitus suppression.

Optical coherence tomography of the cochlea in the porcine model.

OBJECTIVES/HYPOTHESIS: To demonstrate the feasibility of optical coherence tomography in microstructural imaging of the porcine cochlea. STUDY DESIGN: Ex vivo, porcine model. METHODS: Optical coherence tomographic images of the porcine cochlea were obtained by thinning the bone from the basal turn of the cochlea leaving the endosteum intact. The images were compared with the corresponding histological sections. RESULTS: In the areas of thinned bone, images were obtained of the stria vascularis, Reissner's membrane, basilar membrane, tectorial membrane, scala media, scala tympani, and scala vestibuli. The bone was too thick for adequate light penetration in the areas where it was not thinned. Good histological correlation was obtained. CONCLUSIONS: Cochlear and vestibular microanatomic structures of the pig cochlea were clearly identified with histological confirmation, suggesting the potential application of this noninvasive imaging modality for in vivo imaging of the human cochlea.

Unintelligible low-frequency sound enhances simulated cochlear-implant speech recognition in noise.

Speech can be recognized by multiple acoustic cues in both frequency and time domains. These acoustic cues are often thought to be redundant. One example is the low-frequency sound component below 300 Hz, which is not even transmitted by the majority of communication devices including telephones. Here, we showed that this low-frequency sound component, although unintelligible when presented alone, could improve the functional signal-to-noise ratio (SNR) by 10-15 dB for speech recognition in noise when presented in combination with a cochlear-implant simulation. A similar low-frequency enhancement effect could be obtained by presenting the low-frequency sound component to one ear and the cochlear-implant simulation to the other ear. However, a high-frequency sound could not produce a similar speech enhancement in noise. We argue that this low-frequency enhancement effect cannot be due to linear addition of intelligibility between low- and high-frequency components or an increase in the physical SNR. We suggest a brain-based mechanism that uses the voice pitch cue in the low-frequency sound to first segregate the target voice from the competing voice and then to group appropriate temporal envelope cues in the target voice for robust speech recognition under realistic listening situations.