# Study of Electrical Neural Stimulation Effects Using Extraneural and Intraneural Electrodes
## 3 Results

Table 1: Set of stimulation parameters used in the experimental trials [2]. To each current intensity value, a different intensity sensation elicited in the amputee expressed in arbitrary units (a.u.) corresponds. fascicles depends on their number and dimension, their location in the nerve section, and the configuration of active sites. Figure 3: Percentage of activation (PA) vs. fascicle ID for each nerve model (**a–e**) with cuff electrode developed in Comsol Multiphysics. The electric charge values in the bar plot are the corresponding intensities of electric current values used in the experimental human trial. The histogram indicates the axon fiber percentage of activation in each fascicle at a certain electric charge value. Images on the right represent the nerve section of each model and one active site is highlighted to show the side of the stimulation. Each inner fascicle is labeled using a different color that represents the corresponding electric charge intensity observed in the histogram on the left to activate fibers in that fascicle. In Figure 3, it is possible to observe that for some nerve fascicles, when the electric charge intensity increases, no increase in PA is observed (one example is fascicle 1 in Figure 3a for the electric charge values of 720 nC and 960 nC, but analogue observations can be performed for other subplots). Two cases have to be considered related to the fascicles involved: (i) fascicles that have a value below 100% PA; and (ii) fascicles that have values of 100% PA when electric charge values different from the maximum value considered in the experimental study (960 nC) are used. Regarding the first case, we can observe that, for a given fascicle, the PA does not increase, but an increase in PA can be observed in other different fascicles. This behavior can be related to the non-uniform distribution of electric potential into the nerve because of the different electric properties of tissue and the particular location of active sites. Another reason can be due to the threshold process of axons to generate action potentials and as a consequence consider that axon as activated. Probably, the increase in stimulus intensity in some fascicles does not suffice to generate action potential in some axons, and no increase in PA is observed in the corresponding fascicle. About the second case, if one fascicle has a PA of 100%, and there is an increase in stimulus intensity, all the fibers of that fascicle are already activated, so it can be only verified that for other fascicles there is an increase in PA. The simulation results of neural stimulation using a ds-FILE neural electrode are shown in Figure 4, for the corresponding electric charge intensity values used in the experimental trial in a human amputee. In particular, the inner of Figure 4 shows the electric potential color map, in a section plane through the active site, observed in five different nerve models, when the current stimulus is sent by an active site located in the inner of a nerve fascicle. Figure 4 shows the histograms of the fiber's PA related to the electric charge values used in the experimental test on a human amputee (see Table 1). Figure 4: Percentage of activation vs. fascicle ID is shown for five nerve models (**a–e**) that differ in fascicle dimension and position for different values of electric charge that correspond to the electric current intensities used on the human subject. For each histogram, a schematic view of the nerve section is reported to have a reference of the active site involved in the stimulation. Note that the fascicles labeled in _red_ correspond to activated fibers in the histogram. Figure 4a,d show that only the fascicle with the active site located in it has activated fibers above the 10% PA threshold and that the PA increases according to the electric charge intensity. In Figure 4b,c,e, nerve fibers in a single fascicle are activated and the PA has small variations above the threshold value when the stimulus intensity increases.