Effect of Cochlear Implant Electrode Array Design on Electrophysiological and Psychophysical Measures: Lateral Wall versus Perimodiolar Types

Abstract

Background and Objectives The present study aims to investigate whether the cochlear implant electrode array design affects the electrophysiological and psychophysical measures. Subjects and Methods Eighty five ears were used as data in this retrospective study. They were divided into two groups by the electrode array design: lateral wall type (LW) and perimodiolar type (PM). The electrode site was divided into three regions (basal, medial, apical). The evoked compound action potential (ECAP) threshold, T level, C level, dynamic range (DR), and aided air conduction threshold were measured. Results The ECAP threshold was lower for the PM than for the LW, and decreased as the electrode site was closer to the apical region. The T level was lower for the PM than for the LW, and was lower on the apical region than on the other regions. The C level on the basal region was lower for the PM than for the LW whereas the C level was lower on the apical region than on the other regions. The DRs on the apical region was greater for the PM than for the LW whereas the DR was narrower on the apical region than on the other regions. The aided air conduction threshold was not different for the electrode design and frequency. Conclusions The current study would support the advantages of the PM over the LW in that the PM had the lower current level and greater DR, which could result in more localized neural stimulation and reduced power consumption.

Dendritic Degeneration of Human Auditory Nerve Fibers and Its Impact on the Spiking Pattern Under Regular Conditions and During Cochlear Implant Stimulation

“…The mean values of standard deviation (STD) for threshold variations of the investigated electrodes during dendritic degeneration of each TN were 0.22 V for lateral electrode array and 0.07 V for perimodiolar array. Moreover, the perimodiolar array requires a lower threshold than the lateral electrode system in most cases, which is in line with findings in clinical studies (Cohen et al, 2001;Long et al, 2014;Lee et al, 2019).…”

“…Techniques such as electrocochleography, polarity sensitivity, electrically evoked compound action potential (eCAP), and eCAP responses to changing interphase gap are used to evaluate the residual neural health (Santarelli et al, 2008;Garadat et al, 2012;Long et al, 2014;Pfingst et al, 2015;Hughes et al, 2018;Shearer et al, 2018;He et al, 2020). A recent study on lateral and perimodiolar CI systems reported a lower eCAP threshold in the apical region (Lee et al, 2019). Although their findings are in agreement with some studies (Cohen et al, 2001;Parkinson et al, 2002), others found the opposite result for the apical region (Polak et al, 2004;Brill et al, 2009;Van de Heyning et al, 2016).…”

“…In a study of 10 cats, better localized neural excitation for electrodes close to the modiolus compared with the lateral wall was reported (Shepherd et al, 1993). Similar investigations were performed for human subjects that suggest lower threshold, better localization of the nerve stimulations, broader dynamic range, and less channel interactions are possible for electrode array systems close to modiolus compared with those close to the lateral wall of scala tympani (Cohen et al, 2001;Donaldson et al, 2001;Tykocinski et al, 2001;Saunders et al, 2002;Hughes and Abbas, 2006;Lee et al, 2019). In agreement, we showed lower thresholds for the TNs in most investigated electrodes located close to modiolus compared with the lateral array (Table 4).…”

Recent Advances in Cochlear Implant Electrode Array Design Parameters

“…The perimodiolar type offers advantages over the lateral wall type in terms of lower stimulation levels, an expanded dynamic range, and better channel separation. Because perimodiolar configuration provides a placement of electrodes closer to spiral ganglions than the lateral wall, it leads to better neural stimulation, which may result in better speech perception [ 79 ]. Both lateral wall and perimodiolar electrode arrays can cause intra-cochlear trauma, but perimodiolar electrode arrays are likely to deviate to the scala vestibuli from the scala tympani more often than the lateral wall electrode arrays, leading to damage of the osseous spiral lamina/spiral ligament, which can induce new bone formation and ultimately impact the hearing quality [ 77 ].…”

Stimulating the Cochlear Apex Without Longer Electrodes: Preliminary Results With a New Approach

“…However, this option has potential disadvantages, including the increased likelihood of damage to cochlear structures as well as difficulty achieving complete electrode insertion (thus defeating the purpose of a longer electrode). Moreover, longer intracochlear electrodes are typically placed along the lateral wall of the scala tympani rather than in a perimodiolar position; the latter may be more desirable for reducing electrical charge levels, reducing spread of excitation, improving battery life, and producing adequate loudness (11,12). Even with the lateral wall design, the longest electrode on the market only reaches approximately 1.75 out of 2.5 turns into the cochlea, leaving approximately the upper (apical) third of the cochlea unstimulated (6).…”