How Can Individualized Transcranial Alternating Current Stimulation (tACS) Modulate Pain Perception?

Background and aims: The mechanisms through which pain arises from human brain activity have not yet been unraveled. Changes in alpha oscillations, particularly an increase in low-alpha activity, have been consistently reported in those suffering from chronic pain. The main goal of this study is to assess whether there is a causal link between ongoing neural oscillations and pain perception using transcranial alternating current stimulation (tACS) neuromodulation. Methods: We used tACS to modulate ongoing oscillatory activities measured using scalp electroencephalography (EEG). We used sustained and periodic 0.2 Hz thermonociceptive stimuli. The stimulation targeted M1 area of the contralateral dominant hand. The exact frequency of stimulation was set to the individual peak alpha frequency (PAF). A sham stimulation was used as a control condition. Results: Data was acquired from 38 healthy volunteers. Statistical tests were performed using linear mixed models using “time” (pre vs post) and “condition” (active vs sham) as factors. In the “post” phase, we observed a significant reduction in heat pain thresholds (HPTs) compared to the “pre” phase, regardless of condition (p<0.01). The HPT reduction was greater for the sham condition compared to the active condition, although not significantly. Furthermore, both local and global average PAF values decreased significantly (p<0.01) in the two conditions, with a slightly greater reduction in the sham condition. Conclusions: Despite no significant effect of tACS on pain perception, trends of reduced pain and smaller PAF changes in the active condition suggest lower sensitization, indicating potential for further exploration with improved experimental designs.