Statistical analysis
TRD
All statistical analyses were conducted with R v4.2.1 [Functional Connectivity (FC) was calculated as the Pearson correlation coefficient of the brain activity time series pairwise for all 116 × 116 ROIs (seeds). All Pearson correlation coefficients were then transformed into Fisher’s Z scores for further analysis, which are reported as our main FC outcome.To test our primary hypothesis, we first determined which FC pairs were significantly altered by active as compared to sham SNT stimulation from baseline to immediate-post. As a second step, we looked at the relationship between FC changes and clinical changes. Finally, we performed several exploratory analyses: (1) we assessed the sustainability of SNT-induced FC alterations at one-month following treatment, and (2) we compared our TRD group to a healthy control group to determine if there were baseline differences, and if so, whether those differences were affected by SNT treatment.We conducted our statistical analyses as follows:2 (active and sham groups) × 2 (baseline and immediate-post visits) repeated measures ANOVA with statistical significance set at Spearman correlation tests, on the significant group*time interaction FC pairs that survived to Bonferroni correction, between FC changes and absolute MADRS changes from baseline to the immediate-post visit were conducted.Exploratory hypotheses testing on the significant group*time interaction FC pairs that survived to Bonferroni correction. ANOVAs—followed by post-hoc 