Transcranial direct current stimulation (tDCS) refers to a non-invasive brain-stimulation technique that uses electrical current to influence the activity of the brain’s cerebral cortex. The idea behind it is that by increasing or decreasing the activity of specific brain regions, certain brain functions could be enhanced or suppressed. If true, this could open up a number of new and interesting avenues for treating a variety of health conditions, or even enhancing certain cognitive functions – but what does the current science really say about the potential of tDCS? Read on for a breakdown of the evidence behind its purported effects.
Purported Effects of tDCS
In the sections below, we’ll outline some of the early research that has been done on tDCS and its potential effects on a variety of physiological and psychological processes.
However, it is important to keep in mind that the vast majority of this scientific research is still in a very early stage, and a lot more research will be needed before any solid conclusions can be made about the effects of tDCS in healthy human users.
As such, we are not officially recommending or endorsing any of the potential applications of tDCS below, as the science behind them is simply much too preliminary to come to any firm conclusions yet.
As always, none of the information below should be used to replace conventional medical care. If you believe that you might be experiencing any of the symptoms or health conditions discussed below, it is extremely important to talk to your doctor first to obtain an official medical diagnosis and develop an appropriate treatment plan.
It is also important to note that all of the findings below involve tDCS protocols and sessions that were administered by trained professionals, under very specific and controlled settings. In other words, there is no reason to assume that similar effects would be seen by someone using a “home-made” or “D.I.Y.” tDCS device on their own, since any of these particular effects would be highly dependent on exactly where and how the stimulation is being targeted (which only trained experts have the background knowledge to do properly).
With all that in mind, let’s see what some of the recent science has to say about the possible effects of tDCS.
1) May Affect Learning and Skill Acquisition
Some early evidence suggests that tDCS may affect a person’s ability to learn and train new skills.
For example, according to one study, applying tDCS to individuals trying to memorize symbols was reported to improve number processing and numerical abilities, with effects lasting for up to six months after the initial treatment .
Similarly, other studies have reported that when the primary motor cortex was stimulated using tDCS, learning for a motor skill task was improved [2, 3].
One systematic review of data from 13 different studies reported that 3-5 daily sessions of anodal tDCS (applied to the motor cortex) significantly improved motor sequence learning .
According to a study on 104 subjects, tDCS reportedly improved learning rates when applied to the right inferior frontal and right parietal cortex .
Stimulation of the left or right dorsolateral prefrontal cortex (DLPFC) was reported to improve driving abilities in a simulator in 24 volunteers .
While these early results are promising, they also suggest that tDCS probably has to be applied to very specific areas in order to target different particular types of learning and cognitive abilities. More research will be needed to explore these potential effects further.
2) May Affect Pain (in Chronic Pain Conditions)
Many conditions involving chronic pain – such as fibromyalgia, for example – are often difficult to treat. In part, this is because some of the more “common” treatments, such as opioids, often cause undesirable side-effects, and can even have a high risk of leading to addiction.
However, there are some promising early findings that may suggest that tDCS could potentially be used to treat (or at least better-manage) pain in some conditions and circumstances.
For example, according to one randomized controlled trial (DB-RCT) in 48 fibromyalgia patients, five twenty-minute sessions of anodal tDCS applied over the primary motor cortex (M1) reduced pain intensity ratings 30 days after the last treatment .
Similarly, another DB-RCT study in fibromyalgia patients reported that 10 daily sessions of anodal stimulation over the motor cortex resulted in improvement in pain scores and quality of life at both 30 and 60 days post-treatment .
In a smaller crossover study in seven patients with difficult-to-treat chronic pelvic pain, two days of 20-minute tDCS sessions were reported to result in significantly reduced pelvic pain two weeks after treatment .
Finally, one study in patients with chronic pain (due to traumatic spinal cord injury) reported that five consecutive days of tDCS treatment reduced pain by up to 58% in comparison to control treatment .
Nonetheless, while these early results are promising, much more research will be needed before tDCS could become an officially-approved and widespread medical treatment for managing pain.
3) May Affect Language Learning and Abilities
According to two early studies, stimulation of the left frontal lobe with tDCS may contribute to improved language fluency abilities, and may also improve language-based forms of memory [11, 12].
tDCS was also reported to improve performance in language tasks in 3 people with language impairment (aphasia) and improved word retrieval (DB-RCT study) [13, 14]. Additionally, tDCS improved the detection of mismatches in 36 subjects, and enhanced grammar ability in another 50 subjects [15, 16].
4) May Affect Depression Symptoms
Some preliminary studies have suggested the potential of tDCS to help treat or alleviate some of the symptoms of depression.
For example, one study (DB-RCT) in 22 patients with treatment-resistant major depressive disorder applied anodal stimulation to the dorsolateral prefrontal cortex for two weeks. While overall depression scores did not differ between tDCS and placebo groups, the tDCS group reported increased subjective ratings in positive emotions compared to the control group .
Another randomized controlled trial reported that 3 weeks of anodal stimulation in patients with depressive symptoms resulted in significant improvements in mood, attention, and working memory compared to “placebo” tDCS (also known as “sham” treatment, which basically just means fake treatment that doesn’t actually do anything) . However, one patient in this study was reported to develop a mild form of mania, which may suggest some potential negative side-effects of using tDCS to try to treat mood disorders.
While these early findings might sound promising, they are still very preliminary, and much more research will be needed to fully verify the effectiveness and safety of this potential application of tDCS. In the meantime, it is unlikely that tDCS will become a “mainstream” medical treatment for mood disorders anytime soon.
5) May Affect Sleep Quality
In one small study of six individuals with insomnia, tDCS applied to the dorsolateral prefrontal cortex during sleep was reported to improve “sleep efficiency” – meaning that it decreased the amount of time the subjects spent in lighter stages of sleep, while also increasing the amount of time spent in stages of sleep associated with “deeper” sleep .
In another study of 32 patients with post-polio syndrome (a condition developed after suffering from polio and characterized by deteriorating muscle strength endurance), daily anodal stimulation of the premotor cortex for 3 weeks was reported to result in significantly improved sleep quality, vitality, and social functioning in comparison to control treatment .
However, there are several important limitations to keep in mind with these early studies. For one, the sample sizes are still very small, and much larger samples will be necessary to fully verify these preliminary findings. Secondly, some of these studies were only done in patients with specific medical conditions (such as post-polio syndrome), and so it’s not yet clear if similar results would necessarily be seen in otherwise-healthy human users as well.
6) May Affect ADHD Symptoms
ADHD is a condition characterized by increased impulsivity and an inability to focus attention on relevant tasks. Some early research has investigated the potential of tDCS to target and potentially alleviate some of these core ADHD symptoms.
For example, according to one study in 21 male adolescents with ADHD, anodal stimulation with tDCS applied to the right inferior frontal gyrus was reported to significantly improve their ability to ignore irrelevant and competing information on a task designed to test selective attention and information processing (the “flanker” task) .
Another study reported that in nine ADHD individuals, tDCS on the prefrontal cortex improved the speed of processing information as well as the ability to between activities .
Once again, however, these studies have very small sample sizes, and so much more research will be needed to verify and extend these initial preliminary findings.
7) May Affect Recovery in Stroke Patients
Both anodal stimulation to the motor cortex of the affected hemisphere and cathodal stimulation to the motor cortex of the unaffected hemisphere have been reported to improve motor function in one study (DB-RCT) of stroke patients .
Another study investigated the effects of tDCS in 10 stroke patients with stroke-induced aphasia (an inability to understand or produce language due to brain damage from the stroke). This study reported that five days of anodal stimulation of the left prefrontal cortex for 20 minutes significantly improved these patients’ ability to name objects. Although it is not known for sure how long-lasting or permanent these effects might be, these improvements were observed to last up to one week in this study .
Finally, another study examined “sham” (fake) tDCS stimulation in comparison to both anodal and cathodal stimulation of the right and left superior temporal gyrus in stroke patients with aphasia. This part of the cortex contains a region called Wernicke’s Area, a critical brain network involved in the ability to comprehend spoken language. According to this study, 5 weekly tDCS sessions for 2 weeks led to an improvement in verbal comprehension in all of the groups – including the “fake” (control) group! While the cathodal stimulation group showed stronger effects than the other two groups, this interesting pattern of results suggests that at least some of the effects of tDCS might simply be due to the placebo effect .
8) May Affect “Risk-Taking” Behaviors
Cathodal, but not anodal, stimulation to the dorsolateral prefrontal cortex (DLPFC) was reported to reduce risk-taking behavior according to one early DB-RCT study .
In another study, anodal – but not cathodal – stimulation of the DLPFC resulted in significantly reduced preferences for risk in a risk-taking game .
However, while these early results are suggestive of a possible effect of tDCS on risk-taking behavior, much more research will be needed to verify and extend these preliminary findings, and to determine just how significant or relevant they might be.
9) May Affect Reaction Time / Cognitive Processing Speed
One early study in 12 healthy volunteers reported that tDCS applied to the left dorsolateral prefrontal cortex improved verbal reaction times .
While the authors of this study proposed that this effect might be due to increased neuro-plasticity, more research (in much larger groups of participants) will be needed to confirm these findings, as well as to flesh out the underlying mechanisms involved in these potential effects.
10) May Affect Working Memory
Working memory is a type of short-term memory that refers to a person’s ability to hold a set of information in memory, while actively manipulating it.
An example of this would be having to listen to a phone number, then adding ‘1’ to each digit and repeating it back. “Short-term memory” usually refers just to the first part (of memorizing the phone number), whereas “working memory” includes this as well as the subsequent parts (i.e. the cognitive “manipulation” of this information).
A number of early studies have reported that stimulation of the dorsolateral prefrontal cortex may help improve working memory [29, 30, 31].
Interestingly, another study reported that anodal stimulation of the cerebellum did not have any effect on working memory . This finding makes sense since the prefrontal cortex is the part of the brain most commonly linked to higher cognitive abilities (including working memory).
However, many of the sample sizes in these studies were quite small, and it’s also not known how long any of these early reported effects might last – in other words, these “enhancements” might just be temporary, and might not actually enhance overall cognitive performance in any long-lasting or “permanent” way. In any case, much more research (preferably in healthy human users of tDCS) will be needed to confirm these preliminary findings.
11) May Affect (Visual) Attention
According to a few preliminary studies, stimulating the medial-frontal cortex with tDCS may help improve visual attention, as well as improve one’s overall awareness of movement [33, 34].
However, this research is in an extremely early stage, and so these early results will need to be followed up on by a lot more studies to confirm them.
12) May Affect Food and Drug Cravings
Some preliminary research suggests that tDCS may be potentially helpful for managing problematic cravings, such as for junk food or even drugs.
For example, one study reported that tDCS applied to the prefrontal cortex reduced cravings for sugary and high-carbohydrate foods in 19 people, although it had no effect on the amount of food they actually consumed if they did decide to eat them .
Another study applied tDCS to the dorsolateral prefrontal cortex, and reported reduced food cravings in 30 individuals with binge eating disorder (BED), significantly reducing cravings for sweets and savory proteins . Moreover, unlike the previous study described above, in this case, tDCS was also reported to decrease their total food intake by 11%, suggesting that tDCS may have a genuine effect on actual eating behaviors – at least, in some specific populations (such as patients with BED).
Finally, another study (DB-RCT) in 27 smokers reported that single sessions of tDCS applied to the dorsolateral prefrontal cortex over five days resulted in a significant decrease in cravings in response to smoking cues, and even reduced the total number of cigarettes smoked in comparison to the control group .
While these findings are quite interesting and promising, much more research will be needed to fully understand the potential applications of tDCS in managing cravings, and exactly who- and when it might help. In the meantime, it is unlikely that tDCS will become a standard form of treating eating disorders or drug-abuse disorders anytime in the near future.
13) May Affect Parkinson’s Disease Symptoms
Finally, some early evidence has looked at the potential of tDCS to possibly help treat or manage the symptoms of some major neurological disorders, such as Parkinson’s disease.
For example, in one DB-RCT study on eight patients with Parkinson’s undergoing physical training, adding tDCS stimulation on the primary motor and premotor cortex to these patients’ treatment protocols was reported to improve their overall walking speed and balance (two aspects of motor behavior that are often severely disrupted in Parkinson’s patients) .
However, this was only one study so far, and included just eight patients – so a lot more clinical research will be needed to see just how significant the potential effects of tDCS in Parkinson’s disease actually are.
While the research on tDCS and its effects are still in a very early stage overall, some of the early results suggest some interesting future potential.
Nonetheless, most – if not all – of these purported effects and applications will still require extensive additional research to fully confirm and validate them. By extension, at this point, it is relatively unlikely that tDCS will become an officially-approved and widely-used medical treatment in the near future.
Much more research will be needed to determine if any purported “benefits” are actually significant and long-lasting, rather than being merely temporary or based in the “placebo effect.”
Additionally, the overall safety of tDCS in healthy human users – especially its potential long-term effects – has not been well-established.
In conclusion, tDCS offers many promising future avenues of scientific and medical investigation, but is not yet at a stage where it can be adopted for widespread use.