Transcranial direct-current stimulation

Technique of brain electric stimulation therapy

Transcranial direct current stimulation (tDCS) is a form of neuromodulation that uses constant, low direct current delivered via electrodes on the head. It was originally developed to help patients with brain injuries or neuropsychiatric conditions such as major depressive disorder. It can be contrasted with cranial electrotherapy stimulation, which generally uses alternating current the same way, as well as transcranial magnetic stimulation. Research shows increasing evidence for tDCS as a treatment for depression. There is mixed evidence about whether tDCS is useful for cognitive enhancement in healthy people. There is no strong evidence that tDCS is useful for memory deficits in Parkinson's disease and Alzheimer's disease, There is emerging supportive evidence for tDCS in the management of schizophreniaespecially for negative symptoms.

There is some evidence tDCS might be of moderate benefit as treatment for depression.

Recent research on tDCS has shown promising results in treating other mental health conditions such as anxiety and PTSD. 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.

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 minutes 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.) stating 'There is high quality, comparative evidence from the UK that TDCS can improve symptoms of depression and lead to remission' citing new clinical data from Flow Neuroscience

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. Clinical trials are needed to establish the efficacy, feasibility and acceptability of home based tDCS treatment.

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.

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.

tDCS is a CE approved treatment for major depressive disorder (MDD) in the UK, EU, Australia, and Mexico. As of 2015, tDCS has not been approved for any use by the US FDA.