Transcranial Alternating Current Stimulation (tACS) Explained! | Neuroscience Methods 101

Transcranial alternating current stimulation, or tACS is a non-invasive tool to modulate brain waves, which can change behavioral performance. How does it work?
Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation method used in neuroscience research. Rather than increasing brain activity, such as is done by transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS), the goal of tACS is to modulate neural oscillations, also known as brain waves.
A weak alternating current is applied to the head. Although only a small amount of the already weak current reaches the brain, it is enough to affect underlying neurons. tACS is not strong enough to induce neuronal spikes, but it can bias underlying brain cells to fire more rhythmically, in the applied frequency. This is referred to as entrainment.
Indeed, computational studies as well as animal research has shown that tACS can affect neural oscillations. In humans evidence it is more difficult to provide direct evidence. On top of that, results on actual changes in behavioral performance are mixed. Some evidence suggests that tACS can increase motor, perceptual and cognitive performance. But also a lot of null-results are reported. This is likely due to the large inter-individual variability that is related to tACS.
References/resources:
Herrmann, C. S., Rach, S., Neuling, T., & Strüber, D. (2013). Transcranial alternating current stimulation: a review of the underlying mechanisms and modulation of cognitive processes. Frontiers in human neuroscience, 7, 279. doi.org/10.3389/fnhum.2013.00279
Johnson, L., Alekseichuk, I., Krieg, J., Doyle, A., Yu, Y., Vitek, J., Johnson, M., & Opitz, A. (2020). Dose-dependent effects of transcranial alternating current stimulation on spike timing in awake nonhuman primates. Science advances, 6(36), eaaz2747. doi.org/10.1126/sciadv.aaz2747
Klink, K., Paßmann, S., Kasten, F. H., & Peter, J. (2020). The Modulation of Cognitive Performance with Transcranial Alternating Current Stimulation: A Systematic Review of Frequency-Specific Effects. Brain sciences, 10(12), 932. doi.org/10.3390/brainsci10120932
Opitz, A., Paulus, W., Will, S., Antunes, A., & Thielscher, A. (2015). Determinants of the electric field during transcranial direct current stimulation. NeuroImage, 109, 140-150. doi.org/10.1016/j.neuroimage....
Schutter D. J. (2014). Syncing your brain: electric currents to enhance cognition. Trends in cognitive sciences, 18(7), 331-333. doi.org/10.1016/j.tics.2014.0...
Suen, P., Doll, S., Batistuzzo, M. C., Busatto, G., Razza, L. B., Padberg, F., Mezger, E., Bulubas, L., Keeser, D., Deng, Z. D., & Brunoni, A. R. (2021). Association between tDCS computational modeling and clinical outcomes in depression: data from the ELECT-TDCS trial. European archives of psychiatry and clinical neuroscience, 271(1), 101-110. doi.org/10.1007/s00406-020-01...
Narrated by: Miles Wischnewski
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[@samanthasemi8398]

Cool, nicely explained!

[@real.psyched]

Thank you! :)

[@Idkwhattonamess]

Very nice

[@GoatsOut4Justice]

Awesome content thank you!
I'm interested in buying a device to possibly help with depression from ptsd. I'm hoping there's no bad symptoms from it but honestly I'll try anything at this point...
There's some on Amazon that do both tcds and tacs.
I'm wondering do you have any specific devices that you could recommend for me say under $200?

[@real.psyched]

I am afraid that I am not a great source to answer that question. The machines we use in research are very expensive. And I unfortunately know very little about commercially available machines.

[@annmaes7550]

So, if you have anxiety/depression disorder, it means your brain waves are not functioning correctly. Am I correct that a tACS device will make them function normally, but must be repeated daily or several times daily to keep functioning normally?

[@real.psyched]

Currently there are various clinical trials going on testing the effects of tACS on depression and anxiety. It will take a while to convince the FDA, but yes, it seems promising.
Currently, trials try application once a day (20 - 30 min) repeated every day for around 6 weeks.

[@byoung8918]

You might also look for tDCS (Transcranial Direct Current Stimulation) or TMS (Transcranial Magnetic Stimulation). Research papers I have read so far generally support the positive outcome of these stimulations on depression. Depression might not be just about the disorder of brain waves, but also related with functioning of particular regions of brain, like prefrontal cortex.

[@real.psyched]

@@byoung8918 And we got videos on that too!

[@byoung8918]

@@real.psychedgotta check it out :P

[@Klaus.anal.Schwab]

CAN TACS BE APPLIED TO ONLY ONE SIDE OF THE HEAD LIKE THE RIGHT SIDE?

[@real.psyched]

TACS can be applied to multiple locations and both hemispheres. In fact, several current machines allow for multi-electrode montages that target entire brain networks.

[@Klaus.anal.Schwab]

@real.psyched
I have neuromyst tacs, and I was curious to know what the results would be if I applied both of the sponge electrodes to the right side.

[@nilammehta6546]

Could a TENS machine afford similar results?

[@real.psyched]

Not too familiar with TENS units, and there are many different machines. It would be import that the alternating current is ongoing (uninterupted and continuous instead of bursts). Besides that it is import to be able to set frequency and intensity. If a TENS unit can do that, it basically is not different from tACS. But again, I am no expert on TENS

[@12pointlife51]

What is the cost for treatment?

[@real.psyched]

Not sure if anyone provides it as a treatment. There are commercially available tACS devices online.