Related Experiment Video
Updated: Jul 2, 2026
The Combination of Transcranial Alternating Current Stimulation and Electroencephalogram
Published on: October 10, 2025
Phase-synchronized iTBS and tACS at 40 Hz gamma frequency: The impact on working memory performance and functional
Benedikt Glinski1, Min-Fang Kuo2, Kiomars Sharifi3
1Department of Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors, Dortmund, Germany; Department of Psychology, Ruhr-University Bochum, Bochum, Germany.
Background:
Gamma oscillations are critical for cognitive functions. While phase-synchronized electric and magnetic stimulation can boost oscillatory brain activities in theta, alpha, and delta bands, the effects on gamma frequencies have not been investigated yet, especially with respect to functional connectivity and cognitive effects. This study explores how novel non-invasive techniques, phase-locked 40Hz intermittent theta-burst stimulation (iTBS) and 40Hz transcranial alternating current stimulation (tACS), affect working memory performance and associated functional connectivity parameters.
Methods:
Thirty healthy young participants completed five stimulation conditions (1) 40Hz tACS + sham iTBS, (2) 40Hz iTBS + sham tACS, (3-4) two combined interventions (iTBS pulses phase-locked to the tACS peak sine (X-tACS peak) wave or tACS trough sine wave (X-tACS trough), and (5) sham iTBS + sham tACS condition in separate working-memory and resting-EEG sessions, resulting in 10 sessions in total. The target regions were the left and right dorsolateral prefrontal cortices and were stimulated by simultaneous 40Hz tACS and iTBS for 20 min. Working memory performance and functional brain connectivity metrics for local synchronization and global network efficiency were monitored before and after each intervention.
Results:
Only the 40Hz tACS + sham iTBS and 40Hz iTBS + sham tACS protocols enhanced high-load working memory performance speed. The same protocols, along with the X-tACS peak protocol, more pronouncedly improved functional connectivity metrics during the 30 min post-intervention compared to sham, corresponding to the behavioral testing period in separate sessions.
Conclusions:
These results suggest a temporal relation between alterations of functional brain connectivity and working memory task performance.
