Feasibility and tolerability of combining 6 Hz transcranial alternating current stimulation (tACS) at 3.2 mA and digital cognitive training in older adults with mild cognitive impairment.

Transcranial alternating current stimulation (tACS) may enhance cognition and potentiate digital cognitive training (DCT) in mild cognitive impairment (MCI). Optimal intensity remains uncertain because higher currents may increase cortical electric fields but raise tolerability concerns. We evaluated feasibility and tolerability of 3.2 mA tACS plus DCT, and exploratorily assessed active versus sham effects on inhibitory control and cognitive transfer.

Ten older adults with MCI received five daily 6-Hz tACS sessions over the left dorsolateral prefrontal cortex during DCT; ten sham-arm participants from a randomized trial completed identical DCT. Feasibility and tolerability were assessed by adherence, attrition, and side-effect monitoring. Exploratory efficacy used repeated-measures ANOVA with Bonferroni-corrected paired comparisons. Outcomes included antisaccade total errors, verbal and visual memory, and visuoconstructive abilities.

All participants completed treatment (100% adherence). Active-session side effects were mild in 67% and moderate in 23%; no severe events occurred. Side-effect burden was unrelated to DCT performance (p = 0.22). Antisaccade total errors showed a group × time interaction (p = 0.028), favoring active stimulation. Reaction time showed no stimulation-specific effects. Verbal and visual memory showed time effects (p = 0.016 and p = 0.002), whereas visuoconstructive abilities showed a trend-level group × time interaction favoring active stimulation (p = 0.054).

Higher-intensity tACS plus DCT was feasible and well tolerated in older adults with MCI. Exploratory findings suggest that active stimulation may improve inhibitory control and facilitate transfer to selected cognitive domains. Confirmation in the ongoing randomized controlled trial is warranted.