Abstract
We measured the sustained neural response to electrical stimulation by a cochlear implant (CI). To do so, we interleaved two stimuli with frequencies F1 and F2 Hz and recorded a neural distortion response (NDR) at F2-F1 Hz. We show that, because any one time point contains only the F1 or F2 stimulus, the instantaneous nonlinearities typical of electrical artefact should not produce distortion at this frequency. However, if the stimulus is smoothed, such as by charge integration at the nerve membrane, subsequent (neural) nonlinearities can produce a component at F2-F1 Hz. We stimulated a single CI electrode with interleaved sinusoids or interleaved amplitude-modulated pulse trains such that F2 = 1.5F1, and found no evidence for an NDR when F2-F1 was between 90 and 120 Hz. However, interleaved amplitude-modulated pulse trains with F2-F1~40 Hz revealed a substantial NDR with a group delay of about 45 ms, consistent with a thalamic and/or cortical response. The NDR could be measured even from recording electrodes adjacent to the implant and at the highest pulse rates (> 4000 pps) used clinically. We then measured the selectivity of this sustained response by presenting F1 and F2 to different electrodes and at different between-electrode distances. This revealed a broad tuning that, we argue, reflects the overlap between the excitation elicited by the two electrodes. Our results also provide a glimpse of the neural nonlinearity in the auditory system, unaffected by the biomechanical cochlear nonlinearities that accompany acoustic stimulation. Several potential clinical applications of our findings are discussed.
Highlights
For many cochlear implant (CI) listeners, the pathway from implantation to speech comprehension is straightforward
We show that the neural distortion response (NDR) has a group delay of 45 ms, typical of a source in auditory cortex and/or thalamus, and use this response to measure the spread of excitation in the sustained neural response to stimulation of CI electrodes
The ALFIES method described here provides a fast measure of a sustained neural response that can be obtained using the highest pulse rates employed clinically and using a single pair of recording electrodes, even for a recording electrode adjacent to the CI
Summary
For many cochlear implant (CI) listeners, the pathway from implantation to speech comprehension is straightforward. An objective measure of perception could aid the development of new treatments or stimulation methods that are initially tested in animal models, by allowing that evaluation to be performed using the same methods and stimuli as can be employed with humans. Examples of such novel methods include optogenetic and intra-neural stimulation (Middlebrooks and Snyder 2007; Dieter et al 2019) and pharmaceutical interventions designed to improve the fidelity of the neural response (Chambers et al 2017; Carlyon et al 2018)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Journal of the Association for Research in Otolaryngology : JARO
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
