EEG microstates reveal differential network dynamics under constant current and oscillatory brain stimulation

Area of Science:

• Neuroscience
• Brain-Computer Interfaces
• Neuromodulation

Background:

• EEG microstates are brief scalp topographies reflecting large-scale brain network dynamics.
• They may sensitively capture the effects of transcranial electrical stimulation (tES).

Purpose of the Study:

• To evaluate the differential effects of transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS), and oscillatory tDCS (otDCS) on canonical EEG microstates (A-D).

Main Methods:

• A randomized, sham-controlled, crossover study with 42 healthy adults.
• Participants underwent four sessions: tDCS, tACS, otDCS, and sham, with 20-minute stimulation.
• Resting-state EEG was recorded pre- and post-intervention, with microstates (A-D) analyzed for duration, occurrence, and contribution.

Main Results:

• Four canonical microstates explained ~80% of EEG variance.
• All active tES protocols increased microstate A (sensory/arousal), with otDCS showing the strongest effect.
• Microstate B (visual-autobiographical) was suppressed by all active protocols, most by otDCS.
• Microstate C (self-referential) decreased with oscillatory stimulation (tACS, otDCS).
• Microstate D (executive/attention) was enhanced by tACS and otDCS but reduced by tDCS.
• otDCS demonstrated the most widespread and robust modulation, integrating tDCS and tACS effects.

Conclusions:

• Resting-state EEG microstates serve as a sensitive assay for tES aftereffects.
• Constant and oscillatory current waveforms modulate brain network states distinctly.
• otDCS exhibits the most comprehensive modulation, supporting microstates as biomarkers for neuromodulation strategies.