Excitability changes induced in the human auditory cortex by transcranial alternating current stimulation

Transcranial alternating current stimulation (tACS) has been widely studied for its ability to regulate motor, perceptual, and cognitive functions. Given the unique frequency specificity of tACS, it is expected to directly target rhythmic activity in the typical electroencephalogram (EEG) range. After tACS stimulation, changes in stimulation-induced and evoked activities can be inspected. Detecting changes in auditory evoked activity after different frequencies of tACS stimulation will be helpful for further revealing the influence of tACS on the excitation/inhibition of gamma activity in the auditory cortex. Using a randomized repeated measures design, this study assessed the effects of alpha(alpha)-tACS and gamma(gamma)-tACS on the auditory steady-state response (ASSR) in 11 normal-hearing participants. Participants attended four sessions held at least one week apart, receiving tACS or sham treatment. The results indicated that alpha-tACS had an inhibitory effect on 40-Hz ASSR compared to both gamma-tACS and sham tACS, which occurred 30 min after stimulation. Taken together, these findings contribute to the understanding of tACS-induced excitability changes in the human auditory cortex, helping reveal the neuro-physiological changes after tACS.