Neural consequences of 5-Hz transcranial alternating current stimulation over right hemisphere: an eLORETA EEG study

ABSTRACT Introduction Transcranial alternating current stimulation (tACS) at 5-Hz to the right hemisphere can effectively alleviate symptoms of anxiety. The objective of this study was to explore the neural mechanisms that drive the therapeutic benefits. Methods We collected electroencephalography (EEG) data from 24 participants with anxiety disorders both before and after the tACS treatment during a single session. We applied the stimulation over the right hemisphere, with 1.0 mA at F4, 1.0 mA at P4, and 2.0 mA at T8, following the 10-10 EEG convention. With eLORETA, we transformed the scalp signals into the current source density in the cortex. We then assessed the differences between post- and pre-treatment brain maps across multiple spectra (delta to low gamma) with non-parametric statistics. Results We observed a trend of heightened power in alpha and reduced power in mid-to-high beta and low gamma, in accord with the EEG markers of anxiolytic effects reported in previous studies. Additionally, contrary to the widely circulated entrainment theory of the neural effects of tACS, we observed a consistent trend of de-synchronization at the stimulating sites across spectra. Conclusion We confirmed that tACS 5-Hz over the right hemisphere demonstrated EEG markers of anxiety reduction. Regarding changes in power spectra, the effects of tACS on the brain are intricate and cannot be explained solely by entrainment theory.