Alpha‐Oscillatory Current Application Impacts Prospective Remembering Through Strategic Monitoring

TL;DR

Applying alpha-frequency brain stimulation improves future task remembering by affecting brain regions involved in attention and memory.

Contribution

This study shows that alpha-tACS modulates PM performance and neural activity in specific brain regions.

Findings

Alpha-tACS improved prospective memory accuracy compared to sham stimulation.

Alpha-tACS reduced posterior cingulate cortex activity during PM tasks.

Alpha-tACS decreased prefrontal cortex activity during PM compared to working memory trials.

Abstract

Prospective memory (PM) is the ability to remember to execute future intentions. PM requires engagement of attentional networks, in which oscillatory activity in the alpha frequency range has been implicated. The left dorsolateral prefrontal cortex (DLPFC) and inferior parietal cortex are assumed to be engaged during PM tasks. We hypothesized that the selective application of transcranial alternating current stimulation (tACS) at alpha frequency to these areas can modulate PM‐associated event‐related potentials. Participants were assigned to alpha‐tACS, theta‐tACS, or Sham stimulation. They performed a working memory task (OGT), with a PM component, pre‐, during, and post‐stimulation. EEG was recorded post‐stimulation. Accuracy and reaction times (RTs) were computed. Following EEG source reconstruction of mean amplitude, source activity was contrasted between conditions in which performance was modulated by tACS using cluster‐based permutation tests. RTs were slower on introducing the PM task, consistent with strategic monitoring. PM accuracy improved in the alpha‐tACS group only. During PM trials, source activity in the posterior cingulate cortex (PCC) was lower following alpha‐tACS than after Sham stimulation. Source activity in the DLPFC following alpha‐tACS was lower during PM than in OGT trials following alpha‐tACS. Performance modulation through alpha‐tACS, and the lower DLPFC activity in PM than in OGT trials provide evidence of a role for alpha oscillations during strategic monitoring for a PM cue. Lower PCC activity in the alpha‐tACS than Sham group is consistent with facilitation of disengagement of the default mode network, supporting re‐direction of attention from the OGT to the PM task and task‐switching.

Prospective memory (PM) performance and known neural correlates of PM were modulated through application of frontal and parietal transcranial alternating current stimulation at alpha frequency (alpha‐tACS). Alpha‐tACS improved PM accuracy. During PM trials, alpha‐tACS reduced early mean amplitude in the source reconstruction of the posterior cingulate cortex compared to a control group and reduced the late mean amplitude in the source reconstruction of the prefrontal cortex, comparing PM and working memory trials. The findings provide evidence for a role for alpha oscillations in PM processing.

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