Offline 20 Hz transcranial alternating current stimulation over the right inferior frontal gyrus increases theta activity during a motor response inhibition task

Objectives: Previous studies have shown that the right inferior frontal gyrus (rIFG) and the pre-supplementary motor area (preSMA) play an important role in motor inhibitory control. The aim of the study was to use theta frequency transcranial alternating current stimulation (tACS) to modulate brain activity in the rIFG and preSMA and to test the effects of stimulation using a motor response inhibition task.Methods: In four sessions, 20 healthy participants received tACS at 6 Hz over preSMA or rIFG, or 20 Hz over rIFG (to test frequency specificity), or sham stimulation before task processing. After each type of stimulation, the participants performed the Go/NoGo task with simultaneous elec-troencephalogram (EEG) recording.Results: By stimulating rIFG and preSMA with 6 Hz tACS, we were not able to modulate either behavioral performance nor the EEG correlate. Interestingly, 20 Hz tACS over the rIFG signifi-cantly increased theta activity, however without behavioral effects. This increased theta activ-ity did not coincide with the stimulation area and was localized in the fronto-central and centro-parietal areas.