HD-tACS appeared to eliminate age-related impairment in working memory accuracy. After 25 minutes of stimulation, older adults showed a significant increase in task accuracy relative to sham (Fig. 2a), without changing response bias (t41 = 0.770, p = 0.446, dz = 0.119). This behavioral improvement was sufficient to remove the original group difference in working memory accuracy, as older adults after stimulation exhibited a mean accuracy level statistically indistinguishable from that of younger adults at baseline. Further, stimulation had a preferential impact across behavioral metrics. While performance accuracy was boosted following stimulation, we observed no change in mean RT across conditions (Fig. 2a). This suggests that the stimulation-induced benefit in behavioral success was not merely due to subjects trading speed for accuracy between the different stimulation conditions.
