A direct comparison of the electrophysiological effects of transcranial direct and alternating current stimulation in healthy subjects.

Objective: Despite the clinical effectiveness of transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), the comparability of these interventions in neurophysiological aspects have not been thoroughly investigated. Thus, we aimed to directly compare the electrophysiological effects of single-session tDCS and gamma-tACS in healthy subjects, matching the intervention protocol as closely as possible.

Methods: This was a randomized, double-blinded, and active-controlled study. Sixty healthy college students were enrolled in the study. Both tACS with, at 40 Hz frequency, and tDCS have the same current intensity (2 mA, 30 min) within the same target area (right and left dorsolateral prefrontal cortex). Resting-state electroencephalography (EEG) was recorded before and after single-session stimulation.

Results: Significant differences in theta, alpha, low-beta, and gamma frequencies were found between tDCS, tACS, and the sham groups. Low-beta source activity of the middle temporal gyrus was decreased only after an intervention with tACS.

Conclusion: The present study indicates that tDCS and tACS resulted in an increased range of frequency activity, including slow- and fast-wave bands. Specifically, tDCS modulates the frontal region, while tACS modulates neural oscillations at the fronto-central, parietal, and temporal areas. The tACS also decreased low-beta source activity in the middle temporal gyrus. Identifying the common and unique EEG patterns of tDCS and tACS may help shed light on their potential clinical benefits and distinctive neuropathology in various clinical symptoms.