## 3 Results  
To check the changes in relative beta power, relative gamma power, and relative theta power for each brain region, the pre-test measurement values of electroencephalography were covariantly processed with the differences in initial result values. After confirming sphericity with [PERSON]'s test, the two-way repeated measures ANCOVA showed that group differences in IFC-induced beta wave changes were statistically significant (\(p<0.05\)). However, the interactions between group and IFC stimulation were not significant (\(p>0.05\)). The post-hoc analysis of the main effects of relative beta power in each group revealed significant differences in the C3 and P3 regions between the HF-LI and HF-HI groups, as well as between the LF-HI and HF-HI groups (\(p<0.05\); Table 2, Figure 2). [PERSON]'s sphericity test validated that the repeated measures ANCOVA regarding changes in relative gamma waves in each group caused by IFC was statistically significant (\(p<0.05\)). No interaction was observed between groups and time. The post-hoc analysis of the main effects of relative gamma power in each group showed significant differences in the P3 region between the HF-LI and HF-HI groups, as well as between the LF-HI and HF-HI groups (\(p<0.05\); Table 3, Figure 3). Figure 2: Brain mapping of the electroencephalographic (EEG) activity in the \(\beta\)-power band. Left: Scales range from 0.07 (minimum) to 0.59 (maximum) in steps of 0.08. Right: EEG electrodes are depicted in their location on the head, and colors represent the values of relative \(\beta\)-power. Pre-test: before electrical stimulation; Post-test: directly after electrical stimulation; Post-30: 30 min after electrical stimulation; high frequency–low intensity group (HF–LI); low frequency–high intensity group (LF–HI); high frequency–high intensity group (HF–HI). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Variable**} & \multirow{2}{*}{**Group**} & \multirow{2}{*}{**Pre-Test**} & \multirow{2}{*}{**Post-Test**} & \multirow{2}{*}{**Post-Test**} & \multirow{2}{*}{**Post-30**} & \multicolumn{3}{c}{\(F\) (\(P\  
For relative theta power, there was a significant difference in the interaction between group and time in the Fp2, F3, F4, C3, C4, and P4 regions according to the two-way repeated measures ANCOVA with covariate processing of the pre-measured values (\(p<0.05\)). The partial \(\eta^{2}\) values, representing the effects of intervention according to group and time, were 0.188 in the Fp2 region, 0.192 in the F3 region, 0.208 in the F4 region, 0.211 in the C3 region, 0.251 in the C4 region, and 0.229 in the P4 region (Table 4, Figure 4). No significant differences in the main effects were observed after IFC stimulation for relative theta power. Figure 3: Brain mapping of the electroencephalographic (EEG) activity in the \(\gamma\)-power band. Left: Scales range from 0.07 (minimum) to 0.59 (maximum) in steps of 0.08. Right: EEG electrodes are depicted in their location on the head, and colors represent the values of relative \(\gamma\)-power. Pre-test: before electrical stimulation; Post-test: directly after electrical stimulation; Post-30: 30 min after electrical stimulation; high frequency–low intensity group (HF–LI); low frequency–high intensity group (LF–HI); high frequency–high intensity group (HF–HI).