Transcranial direct current stimulation (tDCS) refers to a non-invasive brain-stimulation technique that uses electrical current to influence the activity of the brain\u2019s 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! <\/p>\n\n\n\n\n\n\n\n
Transcranial direct current stimulation<\/em> (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.<\/p>\n\n\n\n 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<\/a> [R<\/a>].<\/p>\n\n\n\n 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 [R<\/a>].<\/p>\n\n\n\n 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.<\/p>\n\n\n\n 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.<\/p>\n\n\n\n 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\u2019t always necessary.<\/p>\n\n\n\n Electrodes are most commonly placed above the motor cortex<\/em>, 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<\/em> (DLPFC).<\/p>\n\n\n\n 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 [R<\/a>].<\/p>\n\n\n\n There are two types of stimulation: anodal<\/em> or cathodal<\/em>. The main difference between the two is their effects on the amount of brain activity (neuronal excitability<\/em>) in the cortical area underneath the site of stimulation. In general, anodal stimulation increases<\/em> the excitability of the neurons the current runs through, while cathodal stimulation decreases<\/em> the excitability of the stimulated area.<\/p>\n\n\n\n One of the most highly-studied effects of tDCS is its purported ability to affect the \u201cmembrane potential<\/em>\u201d of neurons in specific parts of the brain [R<\/a>]. 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<\/em>) – and when it is decreased, the neuron is made less<\/em> excitable.<\/p>\n\n\n\n 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 [R<\/a>].<\/p>\n\n\n\n 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.<\/p>\n\n\n\n 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<\/em> of the reported effects of tDCS may be partly mediated through neuroplasticity<\/em> (the ability of the brain to reorganize connections between neurons over time).<\/p>\n\n\n\n However, most studies that have been done on tDCS haven\u2019t done long-term follow-ups to see how long their effects lasted – and some other studies which have<\/em> 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.<\/p>\n\n\n\n Other suggested mechanisms of tDCS include [R<\/a>]:<\/p>\n\n\n\n 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. <\/p>\n\n\n\n Although some studies may say otherwise, the truth is that the overall safety of tDCS is relatively unknown.<\/strong><\/p>\n\n\n\n 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) [R<\/a>].<\/p>\n\n\n\n Another crucial limitation to be aware of is that the vast majority of studies only look at the \u201cshort-term\u201d 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\u2019t test for the possibility of subtler, \u201clong-lasting\u201d or \u201cchronic\u201d side-effects of tDCS.<\/p>\n\n\n\nHow Does tDCS Work?<\/span><\/h2>\n\n\n\n
Potential Mechanisms of Action<\/span><\/h2>\n\n\n\n
Is tDCS Safe?<\/span><\/h2>\n\n\n\n
An Overview of Safety Data from Studies <\/span><\/h3>\n\n\n\n