tACS applies a weak rhythmic electric current to the scalp. Two or more electrodes are used to pass the electric current from a battery-powered device to the head of the research participant. Most of the electric current travels through the scalp, from one electrode to the other electrode. A fraction of the electric current reaches the brain. The tiny amount of electric current in the brain slightly changes the activity pattern of individual brain cells. Yet, because brain cells are connected to form complex networks, such small changes propagate and amplify each other. Recent research suggests that brain rhythms are particularly susceptible to changes by tACS. The rhythmic electric current interacts with the rhythmic signals generated by the brain. The effect of tACS on brain rhythms is likely strongest when the stimulation current matches the targeted brain activity pattern.
tACS is currently investigated for several clinical indications. All these studies are early pilot studies that are not designed to provide final answers about clinical outcomes of tACS. Also, tACS is not FDA cleared and should not be used outside of the settings of a research study by an experienced brain stimulation scientist.