Effect of the Relative Timing between Same-Polarity Pulses on Thresholds and Loudness in Cochlear Implant Users
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JARO (2020) DOI: 10.1007/s10162-020-00767-y D 2020 The Author(s)
Research Article
Journal of the Association for Research in Otolaryngology
Effect of the Relative Timing between Same-Polarity Pulses on Thresholds and Loudness in Cochlear Implant Users FRANÇOIS GUÉRIT,1,2
JEREMY MAROZEAU,1 BASTIAN EPP,1
AND
ROBERT P. CARLYON2
1
Hearing Systems Group, Department of Health Technology, Technical University of Denmark, 352 Ørsteds Plads, 2800, Kgs. Lyngby, Denmark 2
Cambridge Hearing Group, MRC Cognition and Brain Sciences Unit, University of Cambridge, 15 Chaucer Road, Cambridge, CB2 7EF, United Kingdom Received: 6 April 2020; Accepted: 31 July 2020
ABSTRACT The effect of the relative timing between pairs of samepolarity monophasic pulses has been studied extensively in single-neuron animal studies and has revealed fundamental properties of the neurons. For human cochlear implant listeners, the requirement to use charge-balanced stimulation and the typical use of symmetric, biphasic pulses limits such measures, because currents of opposite polarities interact at the level of the neural membrane. Here, we propose a paradigm to study same-polarity summation of currents while keeping the stimulation charge-balanced within a short time window. We used pairs of mirrored pseudomonophasic pulses (a long-low phase followed by a short-high phase for the first pulse and a short-high phase followed by a long-low phase for the second pulse). We assumed that most of the excitation would stem from the two adjacent short-high phases, which had the same polarity. The inter-pulse interval between the short-high phases was varied from 0 to 345 μs. The inter-pulse interval had a significant effect on the perceived loudness, and this effect was consistent with both passive (membrane-related) and active (ion-channel-related) neuronal mechanisms contributing to facilitation. Furthermore, the effect of interval interacted with the polarity of the pulse pairs. At threshold, there was an effect of polarity, but, surprisingly, no effect of Present address: François Guérit, Cambridge Hearing Group, MRC Cognition and Brain Sciences Unit, University of Cambridge, Cambridge, United Kingdom. Correspondence to: François Guérit & Cambridge Hearing Group, MRC Cognition and Brain Sciences Unit & University of Cambridge & 15 Chaucer Road, Cambridge, CB2 7EF, United Kingdom. email: [email protected]
interval nor an interaction between the two factors. We discuss possible peripheral origins of these results. Keywords: Polarity, Cochlear implants, Inter-phase gap, Inter-pulse interval, Facilitation
INTRODUCTION Cochlear implants (CIs) treat cases of severe-to-profound sensorineural hearing loss by electrically stimulating the spiral ganglion neurons (SGNs). There is a large variability of outcomes across users, with a significant amount of this variability accounted for by the duration of deafness prior to implantation (Blamey et al. 2013). This likely reflects the importance of physiological changes along the auditory pathway fo
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