The neural and behavioral data met the assumptions of the statistical tests used. Data normality was confirmed with the Shapiro-Wilk test (p > 0.05). We used independent samples two-tailed t-tests to examine differences in mean RT on correct trials and accuracy between the different groups of subjects. We used paired sample two-tailed t-tests to examine differences in mean RT on correct trials and accuracy within the same group of subjects between stimulation conditions. To assess within-session behavioral dynamics, we sorted the data from memory blocks into nine sequential 4-minute-long bins (with approximately 4 minutes between each bin from control blocks). To examine changes in behavior at each time bin we used two-tailed t-test. To examine behavioral changes across time bins we used repeated measures analyses of variance (ANOVAs) with the within-subjects factor of time bin (1 vs. 2 vs. 3 vs. 4 vs. 5 vs. 6 vs. 7 vs. 8 vs. 9) and the between-subjects factor of stimulation condition (sham vs. active) or age group (young vs. old).
