# Is there a difference in the spread of excitation at different electrode locations along the cochlea?

## TL;DR

This study found that the spread of excitation in the cochlea is wider in the medial region compared to other areas, regardless of the type of cochlear implant electrode used.

## Contribution

The study provides new evidence on the regional differences in excitation spread in the cochlea during cochlear implantation.

## Key findings

- The medial electrode showed a significantly wider spread of excitation compared to the basal and apical electrodes.
- There were no significant differences in peak amplitudes among the evaluated electrodes in both perimodiolar and straight arrays.
- The findings suggest the importance of objective testing for more effective cochlear implant programming.

## Abstract

To identify whether there are differences in the amplitude and width of spread of excitation (SOE) across the apical, medial and basal regions of the cochlea.

Cross-sectional retrospective study approved by the Ethics Committee of the institution. The study included adults with postlingual deafness, undergoing cochlear implant (CI) surgery, with present intraoperative neural responses in which the SOE was investigated in the basal (6), medial (11) and apical (16) electrodes. Neural response telemetry thresholds, peak amplitudes (µv) of the SOE function and SOE width in millimeters were collected and grouped by the electrode array type for analysis using the Mann Whitney and Kruskal Wallis tests.

Seventy-one subjects were selected, 27 with perimodiolar array and 44 with straight array. There were no significant differences in the peak amplitudes among evaluated electrodes in both groups. However, SOE width (mm) of the medial electrode was significantly wider in both arrays, followed by the width of the basal electrode.

Although the SOE amplitude was similar suggesting similar neural recruitment in different regions of the cochlea, wider spread was found in the medial region even in the perimodiolar array. Thus, the use of objective tests will become increasingly important to assist in CI mapping, aiming for more effective and individualized programming.

Identificar se existem diferenças na amplitude e largura da dispersão da excitação (spread of excitation - SOE) nas regiões apical, medial e basal da cóclea.

Estudo retrospectivo de corte transversal aprovado pela comissão de ética da instituição. Foram incluídos no estudo, adultos com surdez pós-lingual, submetidos ao implante coclear (IC), com presença de respostas neurais intraoperatórias, nos quais a SOE foi investigada em eletrodos representando as regiões basal (6), medial (11) e apical (16) da cóclea. Limiares da resposta neural, amplitudes de pico (µv) e largura da SOE em milímetros foram coletados e agrupados pelo modelo de feixe de eletrodos para análise pelos testes de Mann Whitney e Kruskal Wallis.

Foram selecionados 71 indivíduos, 27 implantados com feixe perimodiolar e 44 com feixe reto. Não houve diferenças significantes nos limiares da resposta neural e nas amplitudes do pico entre os eletrodos avaliados em ambos os grupos. Porém, a largura da SOE do eletrodo medial foi significantemente maior em ambos os feixes, seguida pela largura do eletrodo basal.

Apesar da amplitude da SOE ser semelhante entre os diferentes locais ao longo do feixe de eletrodos, sugerindo recrutamento de populações neurais similares nas diferentes regiões da cóclea, foi encontrada maior dispersão de excitação na região medial mesmo nos eletrodos perimodiolares. Assim, o uso de testes objetivos será cada vez mais importante para auxiliar no mapeamento do IC, visando uma programação mais eficaz e individualizada.