Individual alpha frequency tACS reduces functional connectivity across the default mode network

Structured AbstractO_ST_ABSObjectivesC_ST_ABSResearch on the influence of transcranial alternating current stimulation over alpha functional connectivity (FC) is scarce, and at the same time poses as a potential treatment for various diseases. This study aimed to investigate the effects of individualized alpha frequency tACS (IAF-tACS) on FC within the default mode network (DMN) in healthy individuals, particularly focusing on the precuneus (PCU) as a major hub within the network. Materials and Methods27 healthy participants were recruited, which underwent a 20-minute IAF-tACS session and three magnetoencephalography (MEG) recordings: two pre-stimulation and one post-stimulation. Participants were randomly assigned to either the stimulation or sham group. FC was evaluated through the corrected imaginary phase locking value (ci-PLV) and leakage corrected amplitude envelope correlation (AEC-c). Statistical analyses compared both Pre-Post FC ratio between groups through ratio t-tests and intragroup FC changes through repeated measures t-tests, with FDR correction applied to account for multiple comparisons. An additional analysis simulated the influence of the cortical folding on the effect of tACS over FC. ResultsIAF-tACS significantly decreased AEC-c within the PCU and DMN in the stimulation group compared to the sham group, especially influencing antero-posterior links between hubs of the DMN. No significant changes were observed in ci-PLV connectivity metrics. Negative correlations were found between AEC-c FC changes and power alterations in posterior DMN areas, suggesting a complex interaction between cortical folding and electric field direction. ConclusionsAgainst our initial hypothesis, IAF-tACS reduced FC in the DMN, possibly due to phase disparities introduced by cortical gyrification. These findings suggest that tACS might modulate FC in a more complex manner than previously thought, highlighting the need for further research into the personalized application of neuromodulation techniques, as well as its potential therapeutic implications for conditions like Alzheimers disease.