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Electrical stimulation is not a novel therapy; it has been used for ages to cure ailments. Animal electricity was the first source of electrical stimulation. Nile catfish have electrical properties, although it is unknown if (or how) ancient Egyptians used them for medical purposes. Plato and Aristotle discussed the power of the torpedo fish to generate healing effects through its electric discharges.

Scribonius Largus (the physician of Tiberius Claudius Nero Caesar) suggested placing a live torpedo fish on the surface of the scalp to cure a patient’s headache. Anthero, a freed slave of Tiberius Caesar, experienced gutta (probably gout). In the later part of the eleventh century, Ibn-Sidah, a Muslim doctor from Persia, proposed using live torpedo fish to cure epilepsy.

Unlike fish electricity and electrostatic current, DC is a steady flow of electrical charge. These devices progressed from simple galvanic batteries in the 18th and 19th centuries, to vacuum tubes and transistors in the 20th century, and finally to microprocessors and microcontrollers. Priori and his colleagues studied the effects of DC on cerebral cortex excitability using Transcranial magnetic stimulation in 1998 when the use of DC was promoted and the contemporary tDCS was born.

In their search to subjectively probe cortical characterizations of sensorimotor and cognitive functions and improve neurological functions in healthy humans, clinical neurologists, basic neuroscientists, and psychiatrists are turning to tDCS as a reliable alternative. It is important that the scientific community disseminate its discoveries to the public and media, as some regard tDCS as a ‘miracle technology.

In its many forms, brain stimulation therapy has a diverse and rich history. It can range from giving a harmless electrical current to purposely inducing a seizure. Treatment for some serious mental diseases that do not respond to conventional psychotherapy and medication is provided through brain stimulation therapy, which involves the placement of electrodes or magnets in the brain or on the scalp. The techniques for brain stimulation include repetitive rTMS (Transcranial magnetic stimulation), ECT (electroconvulsive therapy), MST (magnetic seizure therapy), and DBS (deep brain stimulation).

Magnetic fields applied to the head can likewise be used to induce electricity, as can other methods of generating electricity. These sorts of therapies are less commonly utilized than medications and psychotherapies; yet, they have the potential to be effective in the treatment of some mental diseases that have not responded to other treatments. Nowadays, inexpensive gadgets such as the Flow headset make it possible to deliver such therapies in the comfort of one’s own home.

Transcranial Direct Current Stimulation (tDCS) is a method of stimulation of the brain that employs a constant, low-intensity, unidirectional flow of current supplied through scalp electrodes to gradually alter brain activity. The goal is to change cortical excitability and function in critical brain regions, and it is believed to work by hyperpolarizing and depolarizing cortical neurons.

There are numerous variables that can be altered in the delivery of tDCS (e.g., stimulation intensity and duration,  electrode size and number, frequency and spacing of treatment sessions, stimulation site,  and waveform), and there is considerable uncertainty regarding the particular mode of administration, the number of therapies required, and the duration of effect required for ideal therapeutic effects. In therapeutic applications, tDCS is typically given for 20-30 minutes per session, with multiple sessions arranged each week for 2-6 weeks. Throughout the process, the patient remains completely conscious and alert.

Typically, a constant current of 1 to 2 mA is delivered. The current provided through tDCS is not adequate as required for initiation of an action potential in a nerve bundle or a neuron; rather, it alters the configuration of already active nerve cells. Consider the central nervous system and/or brain as being stimulated, attempting to accomplish or learn a new thing, and tDCS as a means of enhancing this continuing action. At the level of the function of a nerve cell, tDCS modifies neuron firing and biochemical transmission of synapses among nerve cells by enhancing synaptic plasticity, which is the biological foundation for learning. tDCS is frequently used in conjunction with training. Training generates synaptic plasticity (learning), and tDCS augments these consequences (improves the plasticity of synapses).

tDCS in the modern era makes use of commercially accessible equipment in the form of small, battery-operated devices. tDCS was previously referred to by other titles, such as ‘brain polarization,’ and frequently required custom-made devices, resulting in less uniform stimulation. It was initially designed to aid individuals suffering from neuropsychiatric disorders or brain injuries including major depression. It is in contrast to cranial stimulation by electrotherapy, which employs AC (alternating current), and Transcranial magnetic stimulation.

There is growing evidence that tDCS can be used to treat depression. There is conflicting proof about the efficacy of tDCS for cognitive enhancement in healthy individuals. There is no compelling evidence that tDCS is beneficial for correcting cognitive deficiencies in Alzheimer’s and Parkinson’s disease, arm or leg function, muscular function in stroke survivors, and non-neuropathic pain. There is rising preliminary level evidence for tDCS for the treatment of schizophrenia – particularly for negative symptoms.

Mechanism of Action. tDCS is accomplished by passing a steady, low-current signal through the electrodes. The current prompts the intracranial flow of biochemical current when the electrodes are positioned in the area of concern. This flow of current then enhances or reduces nerve cell excitability in the region of stimulation, owing to the type of stimulation being used. This change in neuronal excitability results in changes in brain function, that can be employed in various methods of stimulation treatments and to provide additional knowledge on the function of the human brain.

Neurofeedback Therapy to Treat Mental Disorders

Procedure. Transcranial direct current stimulation is a reasonably simple method with only a few components required. Two electrodes are supplied, as well as a battery-operated device that provides a constant current. Additionally, the control software can be utilized in investigations that need multiple sessions with different types of stimulation, such that neither the individual undergoing the stimulation nor even the investigator is able to identify the type. Each device is constructed with a positively charged anodal electrode and a negatively charged cathodal electrode. The term “conventionally” refers to current flowing from the positive anode to the cathode through the conduction tissue between those. It’s worth mentioning that in traditional metal-wired electric circuits, the current is generated by the flow of negatively charged electrons from the cathode to the anode. Conversely, in biological systems such as the cranium, the current is often generated by the passage of ions, which can be positively or negatively charged—positive ions flow toward the cathode, while negative ions flow toward the anode. Both the duration and intensity of the current utilized for stimulation can be controlled by the device.

To prepare the electrodes and the skin for the tDCS device, they must be cleaned. This guarantees that the skin and the electrode have a low resistance connection. The electrode location is critical to the efficacy of the tDCS procedure. The electrode pads are available in a variety of sizes, each with its own set of advantages. A smaller electrode stimulates a single point more precisely, whereas a larger electrode activates the entire area of concern. If the electrode is not properly positioned, it may activate a separate or additional area than expected, resulting in erroneous findings. To complete the circuit, one of the electrodes is placed over the area of interest, while the reference electrode is placed in a different position. This reference electrode is normally positioned on the other side of the body, on the neck or shoulder, from the area of concern. As the area of concern has a small size, it is generally advantageous to locate it prior to implanting the electrode using an imaging technique such as a PET or fMRI to visualize the brain.

Stimulation can commence once the electrodes are appropriately attached. Most equipment has a feature that permits the current to be “ramped up” or gradually increased to the appropriate level. This decreases the amount of stimulation experienced by the person receiving tDCS. After initiating the stimulation, the current will flow for the period indicated on the device and will then be eventually switched off. A unique technique was recently suggested in which, rather than two large electrodes, multiple (more than two) smaller gel electrodes were used to specifically target cortical regions. This revolutionary approach is called High Definition tDCS, and it was observed in a pilot study that HD-tDCS induced significantly larger and more sustained changes in motor cortex activity than sponge tDCS.

Stimulation techniques. Anodal, cathodal, and sham stimulation are the three types of stimulation that occur during the tDCS treatment. Anodal stimulation is a type of positive (V+) stimulation that enhances neuron excitability in the stimulated area. Cathodal (V-) stimulation reduces the excitability of the neurons in the specific area. Cathodal stimulation is a practice that can be used to treat psychiatric disorders caused by an overactive brain area. As a control in tests, mock stimulation is used. Mock stimulation generates a short current that then fades suddenly and there is no stimulation after the initial current for the whole length of the therapy.

The individual getting tDCS is unaware that they are receiving fake stimulation and not continuous stimulation. Researchers can evaluate how much of an effect is attributable to current stimulation and how much is due to the placebo effect by comparing results obtained from individuals who have experienced sham stimulation to those obtained from subjects treated with anodal or cathodal stimulation.

tDCS devices for home therapy. Recently, tDCS devices meant for at-home use have been explored and developed, with applications extending from managing medical problems including depressive illnesses to boosting overall cognitive functioning. More clinical experimental studies are required to determine the feasibility, acceptability, and efficacy of tDCS treatment administered at home.

Studies show that it may be an effective treatment for illnesses like depression, anxiety, Parkinson’s disease, and chronic pain according to several researchers. Some individuals who receive tDCS show cognitive improvement, according to research. The FDA has not yet approved tDCS as a treatment.

Many conditions, including traumatic brain injury (TBI) and stroke, are treated with brain stimulation by neurologists of top institutes around the globe such as the Johns Hopkins Physical Medicine and Rehabilitation department. Brain stimulation is also used to treat symptoms associated with language and mobility disorders, cognitive dysfunction, and long-term chronic pain.

Although tDCS is still a new method of brain stimulation, there are some advantages it may have over other approaches. It is low-cost, painless, non-invasive, and risk-free to use. This treatment is straightforward, and the equipment required to deliver it is lightweight and portable. An itchy or tingly scalp is the most prevalent side effect of tDCS.

tDCS electrically stimulates and activates brain cells. Due to the long-lasting action of tDCS on cortical excitability, it is a useful method for facilitating rehabilitation and treating a variety of neuropsychiatric illnesses. The prompt excitation alters the function of the brain by depolarizing and hyperpolarizing the resting potential of the membrane of the brain nerve cells. When positive stimulation is applied (anodal tDCS), the resting potential of the membrane is depolarized by the flow of current, increasing excitation of the neuron and allowing for enhanced impulse firing by the neurons. When negative stimulation (cathodal tDCS) is applied, due to the flow of current, the resting potential of the membrane is hyperpolarized. As a result of the decreased spontaneous cell firing, this decreases neuron excitability.

When used to treat depression, tDCS currents particularly act on the left side of the frontal lobe’s dorsolateral prefrontal cortex (DLPFC). Left DLPFC has been connected with decreased reactivity in individuals with depression.

A major characteristic of tDCS is the capacity to induce brain alterations long maintenance of the effects of the stimulation after it has been stopped. The period of this alteration is dependent on both the intensity and duration of stimulation. The effects of stimulation become more pronounced as the duration of stimulation or the strength of the current increases. tDCS has been proposed to increase both long-term depression and potentiation, although validation requires additional research.

According to the National Institute for Health and Care Excellence (NICE), the research data on transcranial direct current stimulation (tDCS) for depression presents no significant safety concerns. More than 50,000 people have been treated as suggested in clinical research over the course of more than 50,000 sessions. As far as we know, no major side effects have been reported from using Transcranial direct current stimulation  (i.e., cardiorespiratory arrest, seizures, severe skin burns, electric shocks, hospitalization, death).

As of 2017, itchiness, irritation under the electrode, a phosphene (a transient flash of light that can occur if an electrode is put near the eye and the electrode is turned on) at the commencement of stimulation, nausea, headache, and disorientation are all possible side effects of stimulation lasting up to 60 minutes at a current of up to 4 mA over a two-week period. In the treatment of depression, typical treatment sessions take approximately 20–30 minutes and are repeated on a daily basis for several weeks. As of 2017, there was no information on the long-term side effects of therapy. When electrodes are put above the mastoid for modulation of the vestibular system, nausea is the most common side effect people experience.

People who are sensitive to seizures, such as those who have epilepsy, should not be treated with tDCS. In order to identify the current density at which overt brain injury develops in rats, several studies have been done. Researchers discovered that when the rat was subjected to cathodal stimulation, a current density of 142.9 A/m2, providing a charge density of 52400 C/m2 or greater, resulted in the development of a brain lesion.

Clinical trials for bipolar depression have seen cases of treatment-emergent hypomania and mania as well. In clinical trials, the majority of patients get medication, making it impossible to determine if adverse effects are primarily attributable to tDCS. In a recent meta-analysis, the stimulation was not found to be the cause of the observed treatment-emergent psychosis. A seizure in a child with a background history of infantile spasm and spastic tetraparesis has been reported in a study. However, in this case, it’s uncertain if tDCS provoked the seizure.

When patients are evaluated for appropriate illnesses and stimulation is delivered within specified parameters while using the cautious technique, tDCS has been found to be well-tolerated and safe in studies to date (Aparcio et al., 2016; Bikson et al., 2016; Nikolin et al., 2017). Skin symptoms (irritation, itching, redness) can be avoided with the right treatment strategy. Repeated use of transcranial direct current stimulation has yet to be studied for its long-term consequences.

Depression. tDCS was found safe and effective for treating depression by the British National Institute for Health and Care Excellence (NICE) in 2015. The majority of small randomized clinical trials (RCT) in major depressive disorder (MDD) reported relief from depressive symptoms up until 2014 when the last RCT was conducted. In treatment-resistant MDD, only two RCTs have been performed; both were small, with one finding an impact and the other not.  Compared to sham treatment, one meta-analysis focused on symptom reduction and showed an effect, but another on duplication found no benefit.

Schizophrenia. tDCS has been shown to reduce symptoms by 30% while simultaneously improving a wide range of cognitive abilities (e.g., facial emotion recognition, self-monitoring, facial emotion recognition). Case reports and open-label studies with small samples have formed up the majority of the research to date. In order to prove the efficacy of Transcranial direct current stimulation (tDCS) in schizophrenia, larger randomized controlled studies are required.

Bipolar Disorder. Patients with bipolar depression who received tDCS for one week saw an improvement in their depression symptoms, according to a meta-analysis. TDCS and pharmaceutical treatment were used in one published case study on a male patient suffering from an acute episode of manic depression. Anodal Transcranial direct current stimulation (tDCS) was used in conjunction with a pharmaceutical intervention to treat manic symptoms, and the results lasted for 72 hours following stimulation. In a nutshell, studies have shown that tDCS can help people with depressive symptoms of bipolar disorder.

Disorders Associated With Substance Abuse. The increase in brain activation caused by alcohol-related cues might be inhibited by active tDCS in a short trial with sham controls. tDCS has also been shown to reduce food cravings in patients with disordered eating habits and food addiction triggered by visual stimuli. The therapeutic potential of tDCS in addiction will undoubtedly be further illuminated by a clinical trial presently underway with 340 alcoholic patients and follow-up duration of 24 weeks. As a result of interception in reward networks between prefrontal areas, Transcranial direct current stimulation may have therapeutic effects.

Disorders of Anxiety. Due to the dorsolateral prefrontal cortex’s (DLPFC) involvement in threat processing, tDCS applied to the DLPFC may be a viable therapy option for anxiety disorders. However, empirical data is still scant. Given that exposure-based psychotherapy is the gold standard for treating anxiety disorders, it may also be worthwhile to study noninvasive brain stimulation techniques such as tDCS for their capacity to enhance or augment extinction learning, a critical phase in exposure-based therapies.

Obsessive-Compulsive Disorder. Medication and cognitive-behavioral therapy are being used to manage this disease, however, tDCS may help rectify the abnormality in the functioning of the cortico-striato-thalamocortical neural circuits. The premotor and motor system’s pathological hyperexcitability is reduced, making it a viable alternative to deep brain stimulation, which is currently employed to treat refractory conditions.

Alzheimer’s and Parkinson’s disease. There is inadequate data to support the use of tDCS to treat memory problems associated with schizophrenia, Alzheimer’s disease, or non-neuropathic pain. Some clinical investigations on the use of tDCS to improve memory problems in patients with Alzheimer’s disease, Parkinson’s disease, and healthy participants have yielded inconsistent results. Till 2013, research in schizophrenia discovered that though substantial effect sizes were first observed for improvement of symptoms, subsequent and bigger trials discovered decreased effect sizes. The majority of study has focused on pleasant symptoms such as auditory hallucinations; there is a dearth of research on negative symptoms.

Because the DLPFC is involved in the processing of imminent danger, tDCS administered to the DLPFC may be an effective therapy for anxiety disorders. However, empirical evidence is scarce. In comparison to sham stimulation, Heeren et al. revealed that a single treatment of anodal tDCS for the left DLPFC significantly lowered individuals’ attentional bias for social threat in a probe discriminating test. While tDCS is an attractive method for unraveling the mechanisms involved in social anxiety disorders, the authors believe that drawing definitive conclusions on tDCS-based therapy would be speculative. Considering that exposure-based psychotherapy is the standard method for treating anxiety disorders, it may be important to investigate the capacity of noninvasive brain stimulation techniques such as tDCS to increase or augment extinction learning, a vital phase in exposure-based therapies.

The ventromedial prefrontal cortex was chosen as the target area in this investigation because it is important in extinction learning and thus memory retention. The authors discovered that tDCS across the ventromedial prefrontal cortex was more helpful during fear extinction consolidation than during threat/fear elimination learning itself in a recent study with 28 veterans suffering from post-traumatic stress disorder. However, because fear extinction was not examined in the context of specific traumatic events, but rather in a standardized experimental paradigm, conclusions about the efficacy of tDCS in the treatment of post-traumatic stress disorder would also be incorrect.

To summarize, Transcranial direct current stimulation (tDCS) is an exciting new treatment option for anxiety disorders, but results are yet preliminary. The ideal dosing regimen, therapeutic goals, and mechanism of action are unknown at this time. Transcranial direct current stimulation in combination with cognitive-behavioral techniques looks to be a very good match for treating anxiety disorders. 

Major Depressive Disorder (MDD) has a lifetime prevalence of between 6 percent and 12 percent and a yearly prevalence of between 3 percent and 11 percent throughout the world. After one year of antidepressant treatment, approximately 80% of patients experience a recurrence of depressive symptoms, with up to 33% of patients failing to achieve complete remission after two or three pharmaceutical trials. The complexity and heterogeneity of MDD – with variations in its etiology, symptoms, course, and response to treatment – necessitates further investigation that aims to refine our understanding of the underlying neurobiology, with the ultimate goal of identifying circuits and brain areas associated with this pathology.

There is growing evidence that tDCS is effective in the treatment of depression. A consensus of European specialists graded tDCS as a possibly beneficial technology in the treatment of depression in the most recent CANMAT (Canadian Network for Mood and Anxiety Treatments) edition.

Clinical research has shown that tDCS effectively reduces the clinical symptoms of severe depression. One of the first studies to use 1-mA anodal stimulation for 20 minutes a day over the left DLPFC for five days by Fregni et al. showed significant improvement in symptoms. Different stimulation procedures and patient subpopulations were examined in several randomized clinical trials with variable outcomes. Researchers used meta-analyses of randomized clinical studies to show that active tDCS had a greater response and remission rates and improved depression scores in comparison to sham tDCS. One meta-analysis, on the other hand, found no difference between active and sham stimulation groups in terms of response or remission rates. It’s clear that evaluating different stimulation methods and small sample sizes is an issue because the results are so inconsistent.

The results of the efficacy of Transcranial direct current stimulation (tDCS) in treating major depressive disorder are varied due to the variety of patient samples, the intensity of symptoms of depression, and the small sample sizes. Moreover, the combination of stimulation and cognitive tasks is also being investigated as a viable strategy for increasing the efficacy of tDCS for the management of Depression.



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