Cochlear implant re-mapping informed by measures of viability of the electrode-neural interface: a systematic review with meta-analysis.

The electrode to auditory nerve interface (ENI) is often considered a bottleneck for information transmission for listeners using a cochlear implant (CI). Clinically, it could be beneficial to have a CI programming plan based on optimising information flow based on an individual's ENI status. This review explores whether re-mappings informed by the viability of ENI can improve the speech perception (noise and/or quiet) of adult CI users. Six databases (MEDLINE, EMBASE, TRIP, Scopus, Web of Science, CINAHL), were searched in April 2024 to identify studies that compared an experimental CI mapping method informed by an ENI measure with the routine clinical mapping among adult CI users. A customised questionnaire was created modified from established critical appraisal tools to assess the risk of bias. Data was extracted to compute a standardised mean difference between the control and experimental maps (Cohen's d) and its variance for each article. A mixed-effect model was used to estimate the combined Cohen's d. Linear Regressions were used to probe potential interactions. Thirty articles, mostly within-subject map crossover studies and one RCT, were included. Re-mappings informed by ENI yielded a moderate and significant effect size of 0.48 on speech-in-noise perception. Looking into subgroups, site selection interventions yielded a moderate and significant (p = 0.005) effect size of 0.59. Some site selection interventions were particularly successful while being informed by the low-rate threshold, modulation detection threshold, and electrode discrimination, yielding large and significant effect sizes around 1-1.5. Interventions aiming to reduce the Frequency-to-Place Mismatch by altering the frequency allocation yielded an insignificant (p = 0.32) effect size of 0.47 due to the large variability between and within studies. The variability of outcomes remains substantial both within and between studies. The same intervention is often conducted by the same research group and hence replications at different labs could further strengthen the result. Based on the synthesised result, re-mappings informed by ENI measure could provide better CI hearing to individuals.