Personalized transcranial electrical stimulation (tES) for modulation of associative memory performance

Abstract

Associative memory (AM) represents an ability to bind unrelated information into meaningful units and encode them as distinct memories. AM has been the function of interest in many non-invasive transcranial electrical stimulation (tES) studies aiming to maximize the potential for memory modulation by varying stimulation loci, frequency, and amplitude. In the current study, we aimed to capture modulation potential of AM performance when tailoring the stimulation protocols to the individual brain rhythms. By matching the stimulation frequency to the frequency of each subject’s AM task induced electrophysiological activity in theta spectrum (4-8 Hz), we developed two types of personalized oscillatory protocols: otDCS and tACS, which we administered alongside the constant tDCS and a sham condition in the single-blind cross-over experiment. To comparatively assess the effects of different tES protocols delivered over the posterior parietal cortex, we tested the recognition and recall ability of the 42 healthy young adults on paired-associate paradigms after each of four conditions. Conditions were administered week-apart in a counterbalanced order. Group level comparisons of each active tES condition against sham did not show differences in AM performance either on recognition or cued-recall. However, data showed variability in performance depending on the task and the outcome measures, which calls for stratified approach in order to test robustness of observed findings. Apart from introducing a novel approach to probing AM with personalized tES, this well-powered, multi-protocol, multi-task and multi-measure study produced a comprehensive dataset that allows exploration of factors that could uncover different patterns in responsiveness to tES.