Personalized brain stimulation based on brain oscillations: A systematic review of MEG- and EEG-informed transcranial alternating current stimulation (tACS).

OBJECTIVE

Transcranial alternating current stimulation (tACS) provides promising evidence as a technology to modulate brain oscillations. Individualized brain oscillation measures from magnetoencephalography (MEG) or electroencephalography (EEG) (M/EEG) can optimize frequency, location (montage), and timing of tACS. This systematic review aims to comprehensively characterize the parameter space and outcomes of M/EEG-informed personalized tACS interventions.

METHODS

We conducted a systematic review of the literature up to January 2024, per PRISMA guidelines. The pre-registered search strategy combined terms related to M/EEG and tACS. Any study that utilized M/EEG-informed individualized tACS intervention was included, and relevant variables were extracted.

RESULTS

Seventy-eight publications comprising 143 distinct experiments were identified, including 128 EEG-informed and 15 MEG-informed studies. Frequency-based individualization was predominant (93%), followed by timing-based (4.2%; stimulation onset or phase) and montage-based (2.8%) methods. The most frequently individualized frequency band was alpha (69.2%), followed by theta (15.4%), gamma (5.6%), beta (4.9%), delta (2.1%), and dual-frequency protocols (2.8%). Outcome measures most commonly assessed physiological changes (28.7%) and cognitive functions, particularly perception (18.9%) and memory and learning (17.5%). 77.9% of sham-controlled experiments reported significant positive outcomes, compared to 56.2% of those with active control.

CONCLUSION

Over the past decade, personalized M/EEG informed tACS trials provide growing evidence for effectiveness of this technology in engaging brain oscillations. This systematic review highlights key methodological parameter space in this technology and its outcomes. It also provides a roadmap for future trials with rigorous active control arms to optimize engaging brain oscillations and impacting cognitive functions and clinical outcomes.