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A Comparison of Closed Loop vs. Fixed Frequency tACS on Modulating Brain Oscillations and Visual Detection
Heiko I Stecher1, Annika Notbohm2, Florian H Kasten1
1Experimental Psychology Lab, Department of Psychology, European Medical School, Cluster of Excellence "Hearing4all", Carl von Ossietzky University, Oldenburg, Germany.
Frontiers in Human Neuroscience
|July 12, 2021
Summary
A closed-loop transcranial alternating current stimulation (tACS) protocol did not enhance alpha power or visual detection compared to fixed frequency tACS. Fixed frequency tACS, however, did increase post-stimulation alpha power.
Area of Science:
- Neuroscience
- Cognitive Science
- Brain Stimulation Techniques
Background:
- Transcranial alternating current stimulation (tACS) modulates brain oscillations at specific frequencies.
- Fixed stimulation frequencies in tACS may become ineffective if endogenous brain rhythms shift.
- Adaptive stimulation protocols aim to maintain optimal frequency matching for tACS.
Purpose of the Study:
- To investigate if an intermittent closed-loop tACS protocol, adapting to endogenous alpha rhythm frequency, enhances modulation of visual detection and post-stimulation alpha power compared to fixed-frequency tACS.
- To compare the efficacy of adaptive (closed-loop) versus fixed-frequency tACS and sham stimulation on parietal alpha activity and visual perception.
Main Methods:
- An intermittent closed-loop tACS protocol was developed, involving real-time EEG analysis to adjust stimulation frequency between epochs.
- The closed-loop protocol was compared against a classical fixed-frequency tACS protocol and a sham condition in a three-group study.
- The primary target was the parietal alpha rhythm, with outcomes including modulation of visual luminance change detection and post-stimulation alpha peak power.
Main Results:
- Contrary to the hypothesis, the closed-loop protocol did not yield significant improvements in visual detection or alpha power compared to fixed-frequency tACS.
- A fixed stimulation frequency protocol resulted in a significant persistent increase in post-stimulation alpha power compared to sham.
- No significant modulation of visual detection performance was observed in any of the stimulated groups.
Conclusions:
- A fixed stimulation frequency protocol appears more effective for inducing persistent physiological changes, such as increased alpha power, compared to an adaptive closed-loop protocol.
- The current study did not find evidence supporting the superiority of adaptive tACS for enhancing cognitive functions like visual detection.
- Further research is needed to optimize adaptive tACS protocols and investigate behavioral effects more thoroughly.
