What is transcranial Alternating Current Stimulation (tACS)?


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The basics of tACS

Transcranial Alternating Current Stimulation (tACS) is a device that applies a low-intensity sinusoidal electrical current to the brain through electrodes on the scalp. The technique can be painless and is thought to boost the brain's own oscillations, which can be used to treat disease or enhance brain function. In many ways tACS is similar to tDCS as a neuromodulatory technique, but instead of applying a direct electrical current, tACS oscillates a sinusoidal current at a chosen frequency to interact with the brain’s natural cortical oscillations. Generally, a large electrode is placed over an area of interest which applies stimulation while a reference electrode is placed in a neutral location. When a single, low frequency (< 100 Hz) frequency is applied the exogenous oscillation can synchronize with the brain’s endogenous frequency. This is typically what tACS is. When several oscillations are pulsated, desynchronization of cortical oscillations can occur. As such, tACS effects are contingent on the frequency, amplitude, and phase applied. tACS applied in the EEG frequency range (0.1-80Hz) can entrain neural oscillations, augmenting them. In higher ranges (1-5 kHz), oscillation interaction is unlikely to occur, but cortical excitability has been suggested1. tACS has recently become more popular with more clinical trials and even consumer devices, but it has a history that dates back decades2.

How does transcranial Alternating Current Stimulation (tACS) change the brain?

The exact mechanisms of action tACS are still unclear, but the effects are thought to relate to the manipulation of brain oscillations.3 Brain oscillations (or brain rhythms) are always happening in the brain and impact how we think, feel, and relate to brain disease. To change brain oscillations with tACS, is a way to tap into and control brain functions.

What is transcranial Alternating Current Stimulation (tACS) used for?

tACS has been tested in human trials to both treat brain disease and to enhance brain function in health individuals4 Some areas tACS is currently being explored include: Depression5, Parkinson’s, Schizophrenia, tumor retardation, cognitive enhancement, Tinnitus6 , and motor performance. But the regulatory (approval) status of tACS varies depending on the jurisdiction and what it is used for.

Is transcranial Alternating Current Stimulation (tACS) FDA approved?

tACS is not FDA approved for medical use in the USA. This does not mean the USA FDA has any decision on the efficacy or safety of transcranial Alternating Current Stimulation for any use. In the US tACS for medical use is therefore considered “Investigational”. The FDA also does not regulate the practice of medicine, meaning they don't regulate doctors. For this reason many doctors can provide tACS treatments “off-label” provided they follow all other regulations that apply to their practice.
The FDA regulated medical use, for tACS for “wellness” can fall outside any FDA regulation.7 Wellness could be things like generally feeling better, thinking better.

What are the side effects of tACS?

According to clinical trials, the side effects of tACS are relatively mild and short lasting8. They include itching, tingling, and redness under the electrodes and also light flashes of light called phosphenes. All these effects go away after the tACS is turned off. There are other side-effects that have been reported following tACS such as headache but these can occur at the same rate as sham (sugar pill) stimulation, which means they may just randomly happen and so are not a result of tACS.

Is transcranial Alternating Current Stimulation (tACS) safe?

Transcranial Alternating Current Stimulation (tACS) is considered by clinicians and researchers as safe, in the sense that it does not produce any lasting harm.The term Serious Adverse Event is used in clinical trials to describe an unsafe effect, such as one that requires a trip to the hospital. Based on current testing, tACS does not produce serious adverse events.

Is transcranial Alternating Current Stimulation (tACS) and Cranial Electrotherapy Stimulation (CES) the same?

If tACS and CES are the same depends on definitions9. If tACS is defined as using a basic sinusoidal current and CES is a more complex mix of waves, then they are not the same. But if both tACS and CES are defined as stimulating the head with a current of a few mA intensity that oscillates back and forth, then they are the same.

Where can I get tACS?

Getting tACS will depend on where you live and what you want to use it for. There are consumer devices for tACS that can be purchased directly, and there are medical tACS devices that only a doctor or a researcher can use.

The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.




References

1. Antal, A., Boros, K., Poreisz, C., Chaieb, L., Terney, D., & Paulus, W. (2008). Comparatively weak after-effects of transcranial alternating current stimulation (tACS) on cortical excitability in humans. Brain stimulation, 1(2), 97-105.
2. Guleyupoglu B, Schestatsky P, Edwards D, Fregni F, Bikson M. Classification of methods in transcranial Electrical Stimulation (tES) and evolving strategy from historical approaches to contemporary innovations. Journal of Neuroscience Methods 2013; 219: 291-311
3. Reato D, Rahman A, Bikson M, Parra LC. Effects of weak transcranial Alternating Current Stimulation on brain activity – a review of known mechanisms from animal studies. Frontiers of Human Neuroscience 2013; doi 10.3389/fnhum.2013.00687
4. Lang S, Gan LS, Alrazi T, et al. Theta band high definition transcranial alternating current stimulation, but not transcranial direct current stimulation, improves associative memory performance. Sci Rep 2019;9:8562.
5. Alexander ML, Alagapan S, Lugo CE, et al. Double-blind, randomized pilot clinical trial targeting alpha oscillations with transcranial alternating current stimulation (tACS) for the treatment of major depressive disorder (MDD). Transl Psychiatry. 2019;9(1):106. Published 2019 Mar 5. doi:10.1038/s41398-019-0439-0
6. Claes L, Stamberger H, Van de Heyning P, De Ridder D, Vanneste S. Auditory cortex tACS and tRNS for tinnitus: single versus multiple sessions. Neural Plast. 2014;2014:436713. doi:10.1155/2014/436713
7. Bikson M., Grossman P., Thomas C., Zannou A. L., Jiang J., Adnan T., et al. (2016). Safety of transcranial direct current stimulation: evidence based update 2016. Brain Stimul. 9 641–661. 10.1016/j.brs.2017.07.001
8. Matsumoto, Hideyuki, and Yoshikazu Ugawa. Adverse Events Of Tdcs And Tacs: A Review. 2020.
9. Guleyupoglu B, Schestatsky P, Edwards D, Fregni F, Bikson M. Classification of methods in transcranial Electrical Stimulation (tES) and evolving strategy from historical approaches to contemporary innovations. Journal of Neuroscience Methods 2013; 219: 291-311


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