PhD defence by Charlotte Amalie Emdal Navntoft

On 30 November 2020, Charlotte Amalie Emdal Navntoft will defend her PhD thesis: Improving cochlear implant performance with new pulse shapes: a multidisciplinary approach

Time: 14:00
Place: Zoom, register for the defence here:

Principal supervisor: Associate Professor Jeremy Marozeau
Co-supervisor: Associate Professor Tania Rinaldi Barkat

Associate Professor Bastian Epp, DTU Health Tech
Professor Andrej Kral, Hannover Medical University
Professor Johannes Frijns, Leiden University

Chairperson at defence:
Senior Researcher Jens Hjortkjær

The cochlear implant (CI) is a neuroprosthesis for people with a severe to profound hearing loss that do not gain any benefit from a hearing aid. The CI can provide a sense of sound by electric stimulation of the auditory nerve via electrodes implanted in the inner ear. However, the state-of-the-art CI is not perfect. Improvements are needed to help CI users better understand speech in noisy situations, enjoy music, and reduce the great variability in outcome across users. One problem is that the intracochlear electrodes, despite their small size, are not directly coupled to the auditory nerve fibers. As a consequence, each electrode activates not just target nerve fibers nearby, but also nerve fibers further away, considered off-target. One analog is that a normal hearing person hears a piano played with all 10 fingers, while a CI user hears the piano played with boxing gloves.  
In this Ph.D. project, we challenged the current paradigm of how to most efficiently deliver information in the form of electric pulses to auditory nerve fibers. In most commercial CI’s, the electrical stimulation is performed with a rectangular pulse. However, we propose that a pulse shape with a rising, ramped slope might better match the biophysics of auditory nerve fibers. The main goal of the study was to test the hypothesis that ramped pulses provide more (1) efficient and (2) focused stimulation compared to rectangular pulses, using a multidisciplinary approach combining animal physiology and human psychophysics. 
The first study provided a detailed protocol and video demonstration for acute deafening and the cochlear implantation of an electrode array in a mouse as well as the functional recording of electric stimulation with electrically-evoked ABR (eABR). The second study presented the first physiological data on CI-stimulation with a ramped pulse shape in the established animal model. The third study examined the behavioral response to ramped pulses in human CI users. The animal and human study both showed that that less charge, but higher peak amplitude current, was needed with ramped shapes at threshold and supra-threshold levels compared to rectangular pulses. Spatial selectivity was tested in human, but no significant benefit was found with ramped pulses relative to rectangular pulses. 
Overall, these findings contribute to the general understanding of the interface between an electrode and neurons, and may provide a starting point for further research on ramped stimulation strategies for CI’s. In the long run, the outcomes may lead to improvement of performance with CI’s. 


Mon 30 Nov 20
14:00 - 17:00


DTU Sundhedsteknologi