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 safety of tDCS? Read on to learn more about this intriguing brain-stimulation technique, how it might work, what the potential risks and dangers behind using DIY devices are!
What is tDCS?
Transcranial direct current stimulation (tDCS) is a non-invasive technique for stimulating the brain. It involves using a low-intensity direct electrical current to modulate brain activity in certain regions of the cortex. The cortex is the outermost layer of the brain that plays key roles in many diverse cognitive functions related to memory, attention, abstract thinking, language, and more.
The practice of using electricity to stimulate the brain dates back further than you might think, although its inception took on a cruder form than the current protocols used in research today. The first evidence of transcranial stimulation comes from the Roman Empire, when Scribonius Largus, a Roman physician, described how placing live torpedo fish (a type of ray capable of emitting electricity) onto a patient’s head could (supposedly) relieve headaches [1].
The first person to use direct current stimulation in a clinical setting was Giovanni Aldini, who in the early 19th century supposedly used this technique to cure a patient of major depressive disorder – at least, according to accounts by Aldini himself [2].
tDCS later became popular with German psychiatrists in the late 19th century for the treatment of psychotic patients – but due to a lack of consistency among procedures, unclear descriptions of the treatment, and a misunderstanding of certain aspects of tDCS, results from these studies were either inconclusive or highly inconsistent. This led to the abandonment of tDCS in the 1930s until it made a brief reappearance in the 1960s before being abandoned once again – this time likely due to the emergence of new psychiatric drugs, which (it was believed) made tDCS unnecessary.
Finally, it wasn’t until the late 20th century that tDCS emerged once again, with a considerable number of new clinical studies being conducted over the past two decades or so.
How Does tDCS Work?
tDCS involves placing one electrode on the head or scalp over the brain area to be stimulated, and another electrode on the head or neck of the opposite side – and then running a current through them in order to either increase or decrease the activity of the underlying brain region. Sometimes, the electrodes are first soaked in salty water in order to enhance their ability to conduct an electric current, but this isn’t always necessary.
Electrodes are most commonly placed above the motor cortex, the area of the cerebral cortex that is responsible for planning and executing voluntary movements. However, in recent years, more studies have been done with stimulation to the dorsolateral prefrontal cortex (DLPFC).
Although the exact strength of the current can vary from study to study, a somewhat typical range of settings is generally between 1-2 milliamperes (mA), applied for about 20 minutes or less at a time [3].
There are two types of stimulation: anodal or cathodal. The main difference between the two is their effects on the amount of brain activity (neuronal excitability) in the cortical area underneath the site of stimulation. In general, anodal stimulation increases the excitability of the neurons the current runs through, while cathodal stimulation decreases the excitability of the stimulated area.
Potential Mechanisms of Action
One of the most highly-studied effects of tDCS is its purported ability to affect the “membrane potential” of neurons in specific parts of the brain [4]. Membrane potential is the difference in charge between the inside of the cell and the fluid outside the cell, with a typical neuron having a resting potential of about -70 mV. When the membrane potential is increased (made more negative), the neuron fires more readily (often referred to as increased excitability) – and when it is decreased, the neuron is made less excitable.
Anodal stimulation will tend to increase the membrane potential, thus increasing the excitability of the neurons affected, whereas cathodal stimulation will, in general, decrease the membrane potential, thus decreasing the excitability of the region being targeted [4].
While the electrical and physical mechanisms of the stimulation are fairly well-understood, the precise manner in which these mechanisms might produce noticeable cognitive or psychological effects remains largely unknown. However, a few possibilities have been suggested.
In some cases, the effects of tDCS have been reported to last up to several months after the initial use of the therapy. This may suggest that at least some of the reported effects of tDCS may be partly mediated through neuroplasticity (the ability of the brain to reorganize connections between neurons over time).
However, most studies that have been done on tDCS haven’t done long-term follow-ups to see how long their effects lasted – and some other studies which have done this have reported only temporary or shorter-lived effects. In addition to raising questions about whether tDCS has any meaningful long-term impact on brain function, these conflicting results also call into question whether long-term neuro-plasticity might actually be involved in its potential effects at all.
Other suggested mechanisms of tDCS include [4]:
- Stimulating the release of brain-derived neurotrophic factor (BDNF), a protein that helps grow and create new neurons and connections in the brain (a process called neurogenesis).
- Stimulating the release of the neurotransmitter dopamine throughout the brain, and especially the prefrontal cortex.
- Stimulating the creation and activity of neural stem cells (NSCs), which could further support neurogenesis and synaptic plasticity throughout the brain.
However, it is important to note that these effects have not been directly studied or observed in humans, so they remain purely speculative until much more additional research is performed.
Is tDCS Safe?
An Overview of Safety Data from Studies
Although some studies may say otherwise, the truth is that the overall safety of tDCS is relatively unknown.
For example, nearly all of the individual studies on the safety of tDCS have looked only at very specific forms of stimulation (such as specific voltages, applied to specific parts of the brain) [5].
Another crucial limitation to be aware of is that the vast majority of studies only look at the “short-term” safety: usually, this means checking for side-effects only over a few hours or days from the time of use. However, this means that most studies don’t test for the possibility of subtler, “long-lasting” or “chronic” side-effects of tDCS.
Finally, another major limitation is that when it comes to clinical studies on tDCS, “safety” is very often defined simply as “doesn’t have any immediately obvious and major side-effects” [6]. Note how this doesn’t mean quite the same thing that the average person probably thinks of when they think of something as being “safe,” which usually has more to do with both short-term and long-term risks and dangers!
Therefore, while you can find some studies that claim that tDCS is “safe,” the reality is these studies don’t apply as broadly as they might seem at first glance. At the end of the day, unless you can find a study that specifically tested the safety of the exact same stimulation protocol that you yourself are using – and if it was a long-term study that also did follow-up testing for any potential long-lasting side-effects – then the safety of any particular tDCS protocol should be considered unknown.
Professional vs. “Homemade” or “D.I.Y.” tDCS
Another very important thing to keep in mind is that tDCS should only be administered by a qualified professional under a properly-controlled setting.
Unfortunately, many people attempt to use tDCS on themselves by building their own devices by themselves. This is particularly the case within the “nootropics” community, where people often use experimental supplements, compounds, and techniques to try to enhance their own cognitive abilities or potential. This “home-brew” or “D.I.Y.” (“Do-It-Yourself”) approach can come with many potential risks and dangers.
One of these dangers includes not controlling the voltage and/or current levels precisely enough. This means that a person might not actually know for sure what level of stimulation they are giving to their brain, which could open up the risk of unwanted effects or other adverse reactions. In especially severe cases, using a home-made tDCS device could even lead to electrical shocks, burns, and other harmful consequences.
Another major drawback of using “D.I.Y.” tDCS devices is a lack of appropriate electrode placement. The scientists who design and run experiments on tDCS are extremely knowledgeable in the anatomy and function of the brain – and therefore they are very deliberate about exactly where they target their tDCS stimulation, as well as how strong it is and exactly how long the stimulation sessions last.
People who try to apply tDCS to themselves often lack this knowledge, which essentially means that they’re just randomly stimulating some part of their brain, hoping to get a specific cognitive effect! Clearly, this is extremely unlikely to work out, except by pure chance.
Therefore, the only way to ensure proper tDCS administration is to seek out a qualified professional. While this practice is not extremely widespread yet, it is often possible to find local groups of medical practitioners or other mental health research professionals who offer this service to the public. Therefore, if you are interested in trying tDCS out for yourself, we recommend doing some research to find local professionals – otherwise, we do not recommend trying this out on your own at home.
Side-Effects and other Potential Risks of tDCS
Reported Side Effects
Because tDCS is a broad category that applies to many different levels of voltage and current, and many different specific sites of stimulation in the brain, it’s hard to come to any general conclusions about the overall safety of tDCS as a whole.
On the plus side, the authors of one large-scale review have suggested that – in theory – most of the known dangers of applying electrical stimulation to the head and cortex would have to involve levels of electrical current that are generally much higher than those typically used during most tDCS protocols [6].
While this is slightly heartening news, the fact remains that the safety of the many different individual tDCS protocols out there has not been specifically or directly studied – and so at this time, it is not possible to come to any firm or definitive conclusion about the overall safety of this brain-stimulation technique as a whole.
This general lack of safety information also means that we don’t know as much as we should about the potential side-effects involved in tDCS.
Nonetheless, based on some of the preliminary studies so far, some of the potential side-effects of using tDCS may include [7, 8]:
- Headaches
- Nausea
- Fatigue
- Insomnia / other sleep issues
- Lingering sensations of itchiness and/or “tingling”
- Skin burns, or persistent “burning sensations” (even in the absence of any “real” skin burn)
Although rarer, a number of more serious side-effects have occasionally been reported, such as [5, 8]:
- Seizures
- Psychotic symptoms
Additionally, some preliminary findings suggest that people with pre-existing mood disorders (such as depression) or other psychiatric conditions may be at especially higher risk of experiencing these more-severe side-effects [5, 8].
Some researchers have also raised concerned that tDCS may damage pacemakers. While some studies have found no negative effects on pacemakers, only certain models and types of pacemakers have been tested [9]; therefore, caution is highly advised for anyone with a pacemaker.
Finally, some researchers have also suggested the possibility of “indirect” consequences of tDCS on regions immediately surrounding the ones being stimulated. The idea is that while the stimulation of one specific brain area could theoretically provide certain benefits in one particular cognitive function, it could also interfere with the cognitive functions of the other surrounding areas at the same time. While this possibility hasn’t been experimentally verified, it does raise additional questions about whether the purported effects of tDCS might actually be “benefits” per se, or if they might instead come with important negative trade-offs in other areas of cognition.
Takeaway
Early tDCS studies suggest some interesting future potential, but it’s still uncertain whether tDCS will ever become an officially-approved and widely-used medical treatment.
Furthermore, all purported effects only apply to tDCS that is administered by trained and qualified professionals. Unfortunately, some people attempt to give themselves tDCS treatments “at home” using “home-made” or “D.I.Y.” tDCS machines. This approach carries substantial risks and potential dangers and is not recommended.
Additionally, the overall safety of tDCS in healthy human users – especially its potential long-term effects – has not been well-established, and many important questions still remain. Much more research will be needed to determine exactly which stimulation parameters and techniques are safe.
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 as a conventional medical treatment.
