CP5-Centered Parietal HD-tACS Is Associated with Improved Performance in a Smartphone-Based Shopping Task in Older...

Older adults often experience difficulties in smartphone use, especially when digital tasks require goal maintenance, visual search, sequential action, and response verification. Working memory and parietal theta-band activity may support these cognitively demanding operations, but it remains unclear whether a single session of theta-frequency high-definition transcranial alternating current stimulation (HD-tACS), centered over CP5 as a parietal scalp location intended to approximate the left inferior parietal region, is associated with short-term changes in smartphone-task performance in aging.

This study examined performance in a controlled smartphone-based shopping task and exploratory post-stimulation EEG correlates. In Experiment 1, 40 older adults were randomly assigned to active HD-tACS or sham stimulation. In Experiment 2, 28 older adults completed a reduced-trial EEG extension of the same task with electroencephalography (EEG) recording before and after stimulation.

Active stimulation improved smartphone-task performance, including faster completion under high cognitive load, higher target selection accuracy, and reduced difficulty-time slope. Working-memory performance on a two-back task was also improved, and individual differences in working-memory gains were associated with improvements in smartphone-task efficiency. Active HD-tACS most strongly improved target selection accuracy, and exploratory post-stimulation theta-power changes in posterior/parietal regions may have accompanied high-demand target-selection-accuracy improvement. These neural findings should be interpreted cautiously because the omnibus EEG effects were trend-level, EEG-behavior correlations were based on a small active-stimulation subgroup, data-quality sensitivity analyses indicated artifact-related instability in theta-power estimates, and the full exploratory EEG-behavior correlation matrix did not survive FDR correction.

These findings provide short-term behavioral evidence that CP5-centered parietal HD-tACS may support performance in a cognitively demanding smartphone-based task and motivate further work at the intersection of neuromodulation, cognitive aging, and human-technology interaction.