## 4 Discussion
The measured impedance variation dropped with frequency for all conductivity values based on the highest frequency sample, as shown in Figure 7 for all subplots. The reason there was no significant difference in impedance variation may be associated with the fluid in the ST as this layer is only filled with perilymph fluid. It has been shown that the impedance differences obtained due to complex and diverse internal tissues and anatomical compositions of the human body [34]. This was also proved by Figure 8.  
The modeling results suggested that the outcome for the QS method and TS method were identical for simulation frequency samples from 10 Hz to 10 MHz. Thus, the electrode impedance insertion guidance can be used for this defined frequency range by neglecting the capacitive effect without inducing any errors in the results. The induced electrical potential variation at the border of the ST (outer wall) significantly increased for the highest frequency sample, as shown in Figure 9. However, there was no distinguishable difference in the results for the QS and TS methods based on 10 Hz and 10 MHz samples. This may be proved that the electrical current penetrated the cochlea wall after a certain frequency value (e.g., 10 MHz). This may be used as a threshold frequency level to stimulate all nerve fibers in the vicinity of the ST for better hearing outcomes. The electrical impedance of the biological tissue depends on the tissue composition, tissue anatomy, and frequency of the applied signal [21]. Thus, the current penetration and conduction paths significantly change with frequency. Since the applied current penetrates easily towards the inner structure of the cochlea layers based on the TS method (due to higher frequency levels) compared to the QS method, the electrical potential may induce these layers. Thus, relatively lower impedance values were recorded at the higher frequency due to the higher frequency signal for the TS method, as shown in Figure 5. The applied current was more penetrated towards layers in the vicinity at a higher frequency and induced smooth electrical potential variations compared to the lower frequency simulation based on the TS and QS methods, as shown in Figure 9. The results for both QS and TS methods were identical until 10 MHz. This may be related to the dielectric properties of the cochlea wall as the permittivity of this layer is relatively higher compared to the ST. The current penetrates at higher frequency levels. These effects need to be considered when configuring stimulation protocols in CI patients. This study has several limitations in terms of exploring the effect of the dielectric properties of the cochlea on the impedance variation. Electrode-tissue interface impedance has not been incorporated in simulation models. It has been shown that although changes in the impedance of the electrode-tissue interface directly affect the distribution of the electric field, the voltage distribution in the surrounding tissue remains unchanged [35; 36]. However, the inclusion of nonlinear electrode properties in CI models may provide a more complete picture of electrode-tissue interface stability during long-term stimulation and can help with optimizing electrode design for high electrochemical stability. Second, since the dielectric properties of the ST layer are not available for all frequency levels based on the existing study, it was assumed the ST has similar dielectric properties to the CSF as both layers are composed of fluids. Also, small, discontinuous layers in the cochlea were not included in the cochlea FEM models. This may cause deviations in the electrical potential waveforms but may not affect the maximum measured impedance. Furthermore, the simplified geometrical model was used instead of the anatomical cochlea model to reduce computation cost which may lead to trivial error in the results. However, we believe the overall conclusions of the paper would not change.