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bioRxiv · 10.1101/2024.05.31.596854

Working memory enhancement using real-time phase-tuned transcranial alternating current stimulation

Haslacher, D.·Cavallo, A.·Reber, P.·Kattein, A.·Thiele, M.·Nasr, K.·Hashemi, K.·Sokoliuk, R.·Thut, G.·Soekadar, S.
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Abstract

BackgroundPrior work has shown that transcranial alternating current stimulation (tACS) of parietooccipital alpha oscillations (8 - 14 Hz) can modulate working memory (WM) performance as a function of the phase lag to endogenous oscillations. However, leveraging this effect using real-time phase-tuned tACS was not feasible so far due to stimulation artifacts. Objectives/HypothesisWe aimed to develop a system that tracks and adapts the phase lag between tACS and ongoing parietooccipital alpha oscillations in real-time. We hypothesized that such real-time phase-tuned tACS enhances working memory performance, depending on the phase lag. MethodsWe developed real-time phase-tuned closed-loop amplitude-modulated tACS (CLAM-tACS) targeting parietooccipital alpha oscillations. CLAM-tACS was applied at six different phase lags relative to ongoing alpha oscillations while participants (N = 21) performed a working memory task. To exclude that behavioral effects of CLAM-tACS were mediated by other factors such as sensory co-stimulation, a second group of participants (N = 25) received equivalent stimulation of the forehead. ResultsWM accuracy improved in a phase lag dependent manner (p < 0.05) in the group receiving parietooccipital stimulation, with the strongest enhancement observed at 330{degrees} phase lag between tACS and ongoing alpha oscillations (p < 0.01, d = 0.976). Moreover, across participants, modulation of frontoparietal alpha oscillations correlated both in amplitude (p < 0.05) and phase (p < 0.05) with the modulation of WM accuracy. No such effects were observed in the control group receiving frontal stimulation. ConclusionsOur results demonstrate the feasibility and efficacy of real-time phase-tuned CLAM-tACS in modulating both brain activity and behavior, thereby paving the way for further investigation into brain-behavior relationships and the exploration of innovative therapeutic applications.

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Haslacher, D., Cavallo, A., Reber, P., Kattein, A., Thiele, M., Nasr, K., Hashemi, K., Sokoliuk, R., Thut, G., Soekadar, S.. 2024-05-31. Working memory enhancement using real-time phase-tuned transcranial alternating current stimulation. https://doi.org/10.1101/2024.05.31.596854

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