Working memory after and during 6 Hz transcranial alternating current stimulation
DOI: 10.1192/j.eurpsy.2021.1303
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Summary
This study investigated the efficacy of theta-frequency transcranial alternating current stimulation (tACS) on working memory (WM) performance and resting-state electroencephalogram (EEG) activity. The research was motivated by established evidence suggesting that theta oscillations play a critical role in maintaining information within working memory. The primary objective was to determine whether inducing theta activity via non-invasive brain stimulation could enhance WM accuracy or alter neural oscillatory patterns. The experimental design comprised two distinct experiments. In the first experiment, 31 participants underwent a 20-minute tACS session at 6 Hz with an intensity of 1 mA, applied to Fpz and CPz electrodes, followed by a match-to-sample WM task. The second experiment involved 25 participants assessed across three days to compare after-effects and online effects of stimulation. Participants completed five 25-minute blocks of the same WM task. The protocol included a Training day with no stimulation, a Sham-Verum day (SV) where the first block involved sham stimulation followed by verum stimulation, and a Verum-Sham day (VS) with the order reversed. This design allowed for the assessment of both immediate online stimulation effects and subsequent after-effects on cognitive performance and theta-band spectral power in resting-state EEG. The results indicated that theta-frequency tACS did not produce significant changes in either behavioral or neural measures. In the first experiment, the after-effects of stimulation failed to yield significant alterations in task accuracy or resting-state EEG theta power. Similarly, in the second experiment, 6 Hz tACS delivered prior to the WM task did not generate observable improvements in working memory performance. These null findings extended to online stimulation as well, confirming that neither the immediate application of theta tACS nor its after-effects influenced WM outcomes. The authors concluded that theta-frequency tACS applied to Fpz-CPz electrodes is not an efficient method for improving working memory. These findings challenge the assumption that externally induced theta oscillations via this specific stimulation protocol can enhance WM maintenance. The study highlights the limitations of current tACS parameters in modulating cognitive functions associated with theta rhythms, suggesting that further refinement of stimulation protocols or alternative approaches may be necessary to effectively target working memory processes.
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| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
| discover | success | DOAJ | — | — | 1 | 2026-06-18 |
| archive | success | unpaywall | — | — | 1 | 2026-06-25 |
| extract | success | cached | — | — | 2 | 2026-06-26 |
| clean | success | clean | — | — | 1 | 2026-06-19 |
| chunk | success | chunk | — | — | 1 | 2026-06-19 |
| embed | success | embed | Qwen/Qwen3-Embedding-8B | — | 1 | 2026-06-19 |
| promote | success | — | — | — | 1 | 2026-06-18 |
| summarize | success | llm | qwen3.6-27b-prismaquant | summ-v5 | 1 | 2026-06-26 |
| tag | success | vector_similarity | — | — | 6 | 2026-06-19 |
| verify | success | — | — | — | 1 | 2026-06-26 |
Summary generated by qwen3.6-27b-prismaquant on 2026-06-26; verification: verified.
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