Influence of EZ depth on clinical response to multichannel tDCS. (A) Boxplots illustrate EZN depth determined by averaging the depth of each EZ regions (regions with normalized EI ≥ 0.4) for the responder (R) (In blue) and non-responder (NR) (in red) groups (n = 10 and n = 13, respectively). Each data point corresponds to the mean depth of EZ regions for each patient. The black bar with an asterisk marks a significant difference (pval = 0.025) between R and NR groups using the Wilcoxon test. (B) The scatter plot represents the Spearman correlation coefficient (R = 0.23) between the mean depth of EZ regions and the SF change after multiple cycles of multichannel tDCS.