After effects of tACS on event-related time-frequency data
TACS can change the activity of brain, specifically rhythmic activity. In another study we have shown that the effects tACS can stay even after stimulation has finished (for more information, click here). When we receive a reward or a punishment we also see rhythmic activity of the brain. Rewards and punishments are important for learning. After you do something that leads to a reward, you will likely try it again. Whereas after a punishment you will not repeat that action.
Here we investigated whether tACS can change the rhythmic brain signals related to reward and punishment. However, we looked not at the signals when stimulation was applied. Rather, we wanted to see if these effect persisted even after stimulation ended.
First participant received 15 minutes of tACS at the delta or theta frequency, which are both related to reward and punishment signals. Afterwards, they performed a simple task with two choices. It didn't really matter what they choose, they received randomly reward or punishment feedback. Of course, participants did not know this, they actually thought their choices mattered. Results were compared to a control condition in which participant received placebo (sham) tACS.
We indeed found after-effects of tACS on reward and punishment signals. However, this was only true when tACS was applied at the slower delta frequency. As expected, this did interfere with delta signals in the brain. However, when tACS was applied at the theta frequency, no effects were observed.
Our study showed that tACS can have after-effects on signals in the brain related to receiving rewards and punishments. However, this effect was restricted to one of two brain signals. Since no behavioral outcomes were investigated in this study, we cannot say how this effects learning. This will need to be studied in the future.
You notice that this study is a little nerdy and has no direct implications. However, such fundamental experiments are important too. Based on this study we know we learn more about how tACS works. In future studies we can use this information to more directly study brain and behavior.
Wischnewski & Schutter (2017). After-effects of transcranial alternating current stimulation on evoked delta and theta power. Clin Neurophysiol, 128(11), 2227-2232. https://doi.org/10.1016/j.clinph.2017.08.029