## 4 Discussion  
The development of neuromodulator therapy systems for neurological disorders has accelerated with improved technologies and an expanding understanding of the effect of electrical stimulation on the target tissue layer. The CI neuromodulator provides substantial auditory perception to those with severe or profoundly impaired hearing. However, visual inspection of the progress of electrode insertion is limited and mainly relies on the surgeon's tactile skills. It has been shown that the impedance variation can be used marker of the EA insertion guidance [3; 9; 11]. The available clinical measurement presently provides very limited information, and this may be due to variations in anatomical layers and dielectric properties [3; 13; 15; 26]. It is not feasible to investigate these parameters using experimental methods due to complexity. Computational methods can be used to analyze the impact of such parameters on the electrode insertion guidance based on impedance  
Figure 9: The electrical potential (EP) distributions at the border of the ST based on (**A**) 10 Hz (longest), and (**B**) 100 MHz (shortest) simulation frequency samples. measurement. Most of the bioelectric models of the cochlea only considered the standard dielectric properties of the tissue layers [3; 13; 15]. However, it has been shown that the electrical impedance of body tissues depends on the applied current pulse frequency, thus, more accurate results may be obtained considering the capacitive effect of these layers [17; 18; 19]. Multi-layered cochlea model was developed to examine the impact of the various dielectric properties of the cochlea layers on the impedance measurement using simulation frequency samples. The results for the QS and TS methods were compared to analyze if the capacitive effect can be neglected. The results were simulated and recorded based on center and border EA models. The results for the capacitive effect were examined based on electrical potential variation versus simulation frequency samples (e.g., 1 kHz, 1 MHz, 10 MHz, 100 MHz) using frequency-dependent electrical properties of the cochlea layers. The capacitive effect was clearly visible on the electrical potential waveforms after a certain frequency range for both EA models as shown in Figure 5. When the long current stimulus was used (at 500 us), the electrical potential was increased immediately and continued to grow until the anodic phase of the stimulus was completed. However, the waveform transitions were slower (rounded) due to attenuation of high frequencies. Since the magnitude of the impedance was increased when the EA was placed in the vicinity of the ST, the peak amplitudes were also proportionally changed for all frequency spectrum samples. In particular, the charging/discharging behavior was clearly observed at the start and end of the pulse due to tissue capacitance for the 100 MHz sample. Figure 6 shows the impedance variation was proportional with both EA insertion depth and vicinity to the ST inner wall which is in agreement with both clinical and modeling studies [3; 11]. However, when the simulation frequency was increased, the magnitude of the recorded impedance variation was reduced for all samples. This behavior can be explained by viewing the tissue as a filter. In other words, the measured impedance variation is inversely proportional to the tissue dielectric properties (e.g., conductivity) at higher frequency spectrums based on Equation (2) [33]. Since it is desired to place the EA at the center of the ST layer for the optimal simulation of cochlear implementation, the parametrization dielectric properties of this layer were investigated based on impedance variation. The results for both QS and TS methods were nearly identical apart from some fluctuations. Only a 20% difference in impedance magnitude was observed for the highest frequency sample compared to the remaining.