gms | German Medical Science

Introduction: The electrode to auditory nerve interface is often thought of as a bottleneck for information transmission in cochlear implants (CI): The dynamic range of the transmitted signal is small, only a few electrodes are stimulated along the cochlea, the current spread reduces the neural channel independency, and the health status of the spiral ganglion along the electrode array is also assumed to be varied. Given, the varied factors, is it possible to figure out, which electrodes corrupt the information transmission the most and does disabling them leads to better speech intelligibility?

Methods: A systematic review of the literature (Medline, Scopus, Web of Science) yielded 7,453 articles, of which 16 dealt with electrode deactivation to reduce channel interactions, were published in english language, and compared speech outcomes against a control condition (like the currently clinically used map).

Results: Studies disabling electrodes based on low-rate thresholds, electrode discriminations or modulation detection thresholds showed medium to large effect sizes. Other approaches like partial tripolar stimulation, ECAP IPG effect or multidimensional pitch scaling did not lead to consistent improvements in speech intelligibility (null, negative or small effect sizes). Risk of bias varied between studies.

Conclusions: Remapping based on low rate thresholds, modulation detection thresholds, and electrode discrimination measures were successful in improving speech outcomes. Replication of selected studies among the clinical CI population, especially poor performers are needed.