Utilizing tACS to enhance memory confidence and EEG to predict individual differences in brain stimulation efficacy

Area of Science:

• Neuroscience
• Cognitive Science
• Electrophysiology

Background:

• Successful memory retrieval relies on theta and gamma brain oscillations.
• Previous studies linking oscillations to memory were correlational.
• Noninvasive brain stimulation (NIBS) offers a way to directly test these links.

Purpose of the Study:

• To investigate the direct causal effects of modulating theta and gamma oscillations on memory performance using tACS.
• To determine how externally stimulated brain oscillations influence memory accuracy and confidence.
• To explore if pre-existing electroencephalogram (EEG) measures can predict individual responses to tACS.

Main Methods:

• Participants underwent transcranial alternating current stimulation (tACS) delivering sham, theta (4 Hz), or gamma (50 Hz) stimulation.
• Stimulation was applied over frontoparietal regions during a source memory retrieval task.
• Linear regression models analyzed the impact of tACS on memory accuracy and confidence, alongside pre-stimulation EEG data.

Main Results:

• Both theta and gamma tACS significantly altered memory confidence levels.
• Theta tACS appeared to reduce the confidence threshold for recalled information.
• Gamma tACS influenced the bias associated with memory confidence.

Conclusions:

• Transcranial alternating current stimulation (tACS) can directly modulate memory confidence, not just accuracy.
• Individual differences in tACS efficacy can be predicted by baseline EEG measures.
• EEG may serve as a valuable tool for personalizing noninvasive brain stimulation (NIBS) protocols for memory enhancement.