tACS, transcranial alternating current stimulation, involves using two or more electrodes to send sinusoidal waveforms of electricity onto certain positions of the skull in the hopes that it will change brain function. Some frequencies may need to be combined to get the right effects. Read this post to learn more about the potential benefits and drawbacks of tACS. tACS Brain Stimulation
EEGs (electroencephalography; brain voltage readers) commonly use a Fourier Transformation to convert linear-time sequences of voltage changes in the brain to the domain of frequencies. This is where we get alpha (8-12.5 Hz) for drowsiness, beta (12.5-30 Hz) for alertness, theta (4-7 Hz) for early NREM sleep , and delta (0.1-3 Hz) for deep NREM sleep.
While theta and delta brainwaves are increased by alcohol, beta brainwaves can be increased with LSD , mescaline, and psilocybin [ 1 , 2 ].
In the human brain, there are frequency bands that correspond to ultradian rhythm, a cycle of states of consciousness each with dominant brainwaves. The brainwaves cycle from rest to rest every 100 minutes (with activity between) and from wakefulness to wakefulness every three to eight hours (with drowsiness between) [ 3 ].
Recording and analyzing our own brain signals has the potential to help us schedule our work life on cycles of states of consciousness. This may allow us to work harder in wakeful activity states and take short breaks in resting states and long breaks in resting drowsy states.
May improve memory and learning
Preliminary research suggests it may help with other cognitive functions, pain, schizophrenia, anxiety, withdrawal symptoms, and brain tumors
Insufficient evidence for most benefits
Relatively unknown safety profile
Some adverse effects reported
May increase risk-taking
Health Benefits of tACS
Memory and Learning
Using theta waves on the left parietal area, tACS increased working memory as well as factual memory (or declarative) in 4 clinical trials on 84 healthy people and 12 children with ADHD [ 4 , 5 , 6 , 7 ].
However, this only worked when the theta waves were synchronized (phase-locked) in 2 clinical trials on 28 healthy volunteers [ 8 , 9 ].
tACS may also increase memory confidence , as seen in a small trial on 12 healthy women [ 5 ].
In another trial on 18 healthy people, gamma-tACS improved working memory better than tDCS (transcranial direct current stimulation) and sham [ 10 ].
By using 6 Hz waves on the frontal cortex, tACS improved learning rate in a clinical trial on 50 healthy volunteers [ 11 ].
With the same frequency on the temporoparietal cortex, tACS improved learning new words for 12 older adults [ 12 ].
All in all, limited evidence suggests that tACS may help with memory and learning. Further research is needed to determine how to use it therapeutically. Insufficient Evidence17
The following purported benefits of tACS are only supported by limited, low-quality clinical studies on small populations. There is insufficient evidence to support the use of tACS for any of the below-listed uses until larger, more robust clinical trials are carried out. 1) Changing Brainwaves
As found in 3 different studies on 46 healthy volunteers, tACS significantly increased brainwave power for 30 minutes in the wavelength range used to stimulate the brain after 20 minutes of stimulation [ 13 , 14 , 15 ].With alpha waves (10 Hz), however, it only worked with eyes closed in 2 experiments on 54 healthy people [ 16 ]. 2) Vision tACS at 60 Hz on the visual cortex improved contrast detection in a clinical trial on 12 healthy people [ 17 ].tACS on the parieto-occipital cortex at 10 Hz improved object detection in another trial on 14 people [ 18 ].Gamma-range tACS improves vertical motion detection if it’s placed in the right area according to a test with 45 healthy volunteers [ 19 ]. 3) Movement Gamma tACS improved movement , but beta tACS worsened it, in a clinical trial on 18 healthy volunteers [ 20 ].With 50 Hz, tACS improved motor function in a clinical trial on 15 healthy right-handers [ 21 ].tACS also increased hand-eye coordination at 80 Hz according to a clinical trial on 14 people [ 22 ]. 4) Reaction Times tACS using 10 Hz on the primary motor cortex improved reaction time in 2 clinical trials on 28 healthy volunteers [ 23 , 24 ].Similarly, 40 Hz applied on the right parietal lobe improved conscious reaction time in another trial on 23 healthy right-handed young adults [ 25 ]. 5) Hearing In a study on 9 healthy volunteers, tACS using 35 Hz on the dorsolateral prefrontal cortex improved pitch memory [ 26 ].tACS improved hearing the frequency used for stimulation in another trial on 14 healthy volunteers [ 27 ].As found by a study on 21 healthy humans using 40 Hz on the temples, tACS improved speech perception , thus having a potential for helping dyslexics and learning a new language [ 28 ]. 6) Pain In a clinical trial on 30 people with spinal cord injury, tACS (with a 50 Hz signal) significantly reduced pain [ 29 ].tACS also reduced pain perception in another trial on 23 healthy people, but only when its intensity was unexpected [ 30 ].4 Hz produced pain relief through the mu opioid receptors (acute/ cannabidiol and morphine) while 100 Hz acted through the delta opioid receptor (chronic/cannabidiol) in three animal studies [ 31 , 32 , 33 , 34 , 35 ].At 4 Hz and 100 Hz, tACS reduced pain in mice through alpha 2A adrenaline receptors (the type of pain ignored in fight-or-flight mode) [ 36 ]. 7) Improving Neurochemistry With square waves of 100 Hz put through the earlobes of 38 healthy volunteers, tACS according to a review increased serotonin , beta-endorphin, ACTH , GABA , DHEA , and decreased tryptophan and cortisol in the blood after 20 minutes of stimulation. This suggests tACS might help insomnia and depression [ […]