Phase-synchronized iTBS and tACS at 40 Hz gamma frequency: The impact on working memory performance and functional connectivity

Brain stimulation, vol. 19, pp. 103157

Abstract

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.

Authors 5

1. Benedikt Glinski

   Ruhr University Bochum · Leibniz Research Centre for Working Environment and Human Factors

   Affiliation as printed

   Department of Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors, Dortmund, Germany; Department of Psychology, Ruhr-University Bochum, Bochum, Germany

2. Min‐Fang Kuo

   Leibniz Research Centre for Working Environment and Human Factors

   Affiliation as printed

   Department of Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors, Dortmund, Germany

3. Kiomars Sharifi

   ETH Zurich

   Affiliation as printed

   Department of Information Technology and Electrical Engineering, ETH Zurich, Zurich, Switzerland

4. Michael Andreas Nitsche corresponding

   Bielefeld University · Leibniz Research Centre for Working Environment and Human Factors · Deutsches Zentrum für Psychische Gesundheit

   Affiliation as printed

   Department of Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors, Dortmund, Germany; Bielefeld University, University Hospital OWL, Protestant Hospital of Bethel Foundation, University Clinic of Psychiatry and Psychotherapy, Bielefeld, Germany; German Centre for Mental Health (DZPG), Bochum, Germany. Electronic address: nitsche@ifado.de

5. Mohammad Ali Salehinejad corresponding Aachen Medical Faculty Department of Child and Adolescent Psychiatry

   RWTH Aachen University · Leibniz Research Centre for Working Environment and Human Factors

   Affiliation as printed

   Department of Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors, Dortmund, Germany; Department of Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, Medical Faculty, RWTH Aachen University, Aachen, Germany. Electronic address: msalehinejad@ukaachen.de