Transcranial direct-current stimulation

Depression There is some evidence tDCS might be of moderate benefit as treatment for mild and moderate depression, major depressive disorder and treatment-resistant depression. Other medical use Recent research on tDCS has shown promising results in treating other mental health conditions such as anxiety More research is required on the topic. There is also evidence that tDCS is useful in treating neuropathic pain after spinal cord injury. There is evidence of very low to moderate quality that tDCS can improve activities of daily living assessment in the short-term after stroke. ==Safety==

According to the British National Institute for Health and Care Excellence (NICE), the evidence on tDCS for depression raises no major safety concerns. As of 2017, at stimulation up to 60 min and up to 4 mA over two weeks, adverse effects include skin irritation, a phosphene at the start of stimulation, nausea, headache, dizziness, and itching under the electrode. Typical treatment sessions lasting for about 20–30 min repeated daily for several weeks in the treatment of depression. Adverse effects of long term treatment were not known as of 2017. People susceptible to seizures, such as people with epilepsy should not receive tDCS. Studies have been completed to determine the current density at which overt brain damage occurs in rats. It was found that in cathodal stimulation, a current density of 142.9 A/m2 delivering a charge density of 52400 C/m2 or higher caused a brain lesion in the rat. This is over two orders of magnitude higher than protocols that were in use as of 2009. ==Mechanism of action==

tDCS stimulates and activates brain cells by delivering electrical signals. The lasting modulation of cortical excitability produced by tDCS makes it an effective solution to facilitate rehabilitation and treat a range of neuropsychiatric disorders. The way that the stimulation changes brain function is either by causing the neuron's resting membrane potential to depolarize or hyperpolarize. When positive stimulation (anodal tDCS) is delivered, the current causes a depolarization of the resting membrane potential, which increases neuronal excitability and allows for more spontaneous cell firing. When negative stimulation (cathodal tDCS) is delivered, the current causes a hyperpolarization of the resting membrane potential. This decreases neuron excitability due to the decreased spontaneous cell firing. n addition to localized changes in cortical excitability, tDCS has been shown to influence large-scale brain networks. Rather than affecting isolated regions, stimulation may alter functional connectivity between distributed neural systems, which can contribute to variability in behavioral and cognitive outcomes. In case of treating depression, tDCS currents specifically target the left side of the dorsolateral prefrontal cortex (DLPFC) located in the frontal lobe. Left DLPFC has been shown to be associated with lower activity in the depressed population. tDCS is able to achieve cortical changes even after the stimulation is ended. The duration of this change depends on the length of stimulation as well as the intensity of stimulation. The effects of stimulation increase as the duration of stimulation increases or the strength of the current increases. tDCS has been proposed to promote both long term potentiation and long term depression. ==Operation==

Transcranial direct current stimulation works by sending constant, low direct current through the electrodes. When these electrodes are placed in the region of interest, the current induces intracerebral current flow. This current flow then either increases or decreases the neuronal excitability in the specific area being stimulated based on which type of stimulation is being used. This change of neuronal excitability leads to alteration of brain function, which can be used in various therapies as well as to provide more information about the functioning of the human brain. Clinical trials are needed to establish the efficacy, feasibility and acceptability of home-based tDCS treatment. ==History==

The basic design of tDCS, using direct current (DC) to stimulate the area of interest, has existed for over 100 years. There were a number of rudimentary experiments completed before the 19th century using this technique that tested animal and human electricity. Luigi Galvani and Alessandro Volta were two such researchers that utilized the technology of tDCS in their explorations of the source of animal cell electricity [citation needed]. It was due to these initial studies that tDCS was first brought into the clinical scene. In 1801, Giovanni Aldini (Galvani's nephew) started a study in which he successfully used the technique of direct current stimulation to improve the mood of melancholy patients. There was a brief rise of interest in transcranial direct current stimulation in the 1960s when studies by researcher D. J. Albert proved that the stimulation could affect brain function by changing the cortical excitability. He also discovered that positive and negative stimulation had different effects on the cortical excitability. Research continued, further fueled by knowledge gained from other techniques like TMS and fMRI. ==Comparison to other devices==

In transcranial magnetic stimulation (TMS), an electric coil is held above the region of interest on the scalp that uses rapidly changing magnetic fields to induce small electrical currents in the brain. There are two types of TMS: repetitive TMS and single pulse TMS. Both are used in research therapy but effects lasting longer than the stimulation period are only observed in repetitive TMS. Similar to tDCS, an increase or decrease in neuronal activity can be achieved using this technique, but the method of how this is induced is very different. Transcranial direct current stimulation has the two different directions of current that cause the different effects. Increased neuronal activity is induced in repetitive TMS by using a higher frequency and decreased neuronal activity is induced by using a lower frequency. ==Research==

Depression Determining the safety and effectiveness of tDCS treatment for people with depression is being investigated: • A systematic review of placebo-controlled trials investigating tDCS treatment for major depressive disorder was published 2020. • A 2017 study conducted by Brunoni showed 6-weeks of tDCS treatment resulted in reduction of at least half of depression symptoms in 41% of depressed people (vs. 22% placebo and 47% antidepressants). • In 2015, the British National Institute for Health and Care Excellence (NICE) found tDCS to be safe and to appear effective for depression treatment. Up until 2014, there have been several small randomized clinical trials (RCT) in major depressive disorder (MDD); most found alleviation of depressive symptoms. There have been only two RCTs in treatment-resistant MDD; both were small, and one found an effect and the other did not. One meta-analysis of the data focused on reduction in symptoms and found an effect compared to sham treatment, but another that was focused on relapse found no effect compared to sham. Other reviews found no evidence at all, and evidence from multiple-session tDCS trials. However, the original authors addressed these raised concerns in a further analysis and continued to find no evidence of impact A 2015 review of results from hundreds of tDCS experiments found that there was no statistically conclusive evidence to support any net cognitive effect, positive or negative, of single session tDCS in healthy populationsthere is no evidence that tDCS is useful for cognitive enhancement. Studies on tDCS for gait rehabilitation in Parkinson's patients have also shown mixed results. Research conducted as of 2013 in schizophrenia, has found that while large effect sizes were initially found for symptom improvement, later and larger studies have found smaller effect sizes (see also section on use of tDCS in psychiatric disorders below). Stroke There is no strong evidence that tDCS can help improve upper limb function after stroke. While some reviews have suggested an effect of tDCS for improving post-stroke aphasia, a 2015 Cochrane review could find no improvement from combining tDCS with conventional treatment. Research conducted as of 2013 suggests that tDCS may be effective for improve vision deficits following stroke. However, reproducibility remains to be fully tested across studies and standardization for these kinds of studies has not been implemented fully, though an attempt at formalizing standards was released in 2017. In chronic pain following spinal cord injury, research is of high quality and has found tDCS to be ineffective. tDCS has also been studied in addiction. There is some moderate (level B) evidence to indicate that, in addition to treating major depressive disorder, tDCS may also be appropriate to treat fibromyalgia, and craving disorders. tDCS has been used in neuroscience research, particularly to try to link specific brain regions to specific cognitive tasks or psychological phenomena. The cerebellum has been a focus of research, due to its high concentration of neurons, its location immediately below the skull, and its multiple reciprocal anatomical connections to motor and associative parts of the brain. Most such studies focus on the impact of cerebellar tDCS on motor, cognitive, and affective functions in healthy and patient populations, but some also employ tDCS over the cerebellum to study the functional connectivity of the cerebellum to other areas of the brain. == Limitations ==

While growing literature shows the efficacy of transcranial direct current stimulation (tDCS) for treating nervous diseases such as acute depressive episodes, the lack of knowledge about the nature of this treatment at the cell level While the therapeutic effect is observed in a short period of months, the impact of the electric fields on the brain, specifically on the treated neuronal structures, is a question of further long-term research. Second, tDCS brain tissue stimulation targets a large area of poorly characterized tissue. Therefore, it is unclear whether electrical fields reach only the neural structures of the brain that need treatment. The radiation can destroy healthy cells which don't need treatment during tDCS therapy. ==Regulatory approvals==

tDCS is a CE approved treatment for major depressive disorder (MDD) in the UK, EU, Australia, and Mexico. In December 2025, the company Flow Neuroscience announced that its tDCS device had been approved in the US for standalone or adjunctive treatment of depression at home. == See also ==