Irritation of the lining of the skull through direct current (tDCS), is a non-invasive treatment which exert a weak direct current (1 to 3 mA) on the scalp. Since the direct current with discrete impulses, pays to polarization, not irritated, their work does not directly lead to the firing of action potentials in neurons of the cortex .initial studies in animal models , shows the change activity of cerebral cortex as a result of the passage of electric current for reduce or increase irritability, depending on the electric current passed . These effects with the change in the proteins and intracellular levels of cyclic AMP and calcium, remain for some time , but  they are generally reversible and no effects on the function and structure of cells.

This is also the direct current (DC) electrical stimulation, this method is characterized by the tools that use alternating current (AC) and create discrete impulse stimulation, such as CES, ECT, VNS and DBS. However, tDCS Unlike methods such as rTMS (stimulation cranial wall with electromagnetic waves), is not created stimulate , to the extent  the action potential of response (for example, muscle contraction) . but changes  will guide in order to improve the structure and function of neurons in the desired direction and consider (neuro modulation), so some researchers prefer the term "the direct current polarization cranial wall", and the two terms are equivalent in literature today. this device Is small and portable and usually work with the availability batteries DC .

History electrical stimulation


The first brain stimulation devices were live fish. Romans and ancient Greeks were aware of the obvious shock power catfish Indigo (Nile) and other fish with electric radiation (Electric Ray) (Finger, 2000).  Gallons and  Largus used in Rome the electric fish to treat headaches and various disorders. the fish were probably considered as the first brain-stimulation devices. Romans and Greeks used this fish for the treatment of various disorders. They weather put the fish on the patient's forehead or  ask the paitients to stand on the large number of alive fishes. the fish was unloading its own energy which was not known  as electricity at that time and until after centuries . unfortunately, the fish simply were not available until the cars were built in the eighteenth century which could generate electricity as needed. the early eighteenth century, leading scientists still did not know what substance is streaming into the nerves (Finger, 2000). great thinkers have theorized about the ghosts, special fluids and even swings.   It was Luigi Galvani who laid in a series of experiments that were published in 1791, theory of electric current to the nerve. using primary batteries, he showed that a nerve tested can be activated by electricity and seemly causes the natural muscle contraction. In addition, he announced that the electricity found in nature , can cause a similar response in electrical machines. methods like these were almost start to grow immediately after the start of the practical use of electricity in the late eighties of the nineteenth century. At the time, passing the direct current of the muscles or the brain were common in Europe.

For example, one of Charcot's student Specialties, George Duchamp de Boulogne, along with a small, battery producers will travel to different places in Paris, he was passing electricity from the muscles of patients, and he was testing its effects on numerous disorders and also use it to better understand muscle interventions - especially the nervous and muscular dystrophy (George, 1994). Others have started using the direct current in the brain. That is because this method did not show any benefit, largely as a therapy from his eyes in Europe and America.

The reasons why tDCS remained an active area in Russia, are unclear. in the late 40's. sometimes the "electric sleep therapy" as they said, because patients sometimes, fall sleep within 30 minutes of treatment (Gomez and Michael, 1978). More done tDCS  in Russia do not in Clinical Research and quotes that have been used to treat alcoholism, pain, depression, or a combination of these (Fagner et al., 1973).

Doctor Walter Paulus and his team at Göttingen in Germany, recently became the revival of this technology, active research on tDCS is already done and more than 100 papers published in the last ten years has been approved in magazines. It is clear, tDCS affects the brain and can strengthen the ability of cortical excitability and improves memory in healthy people. , it is not clear yet whether these effects can also be used for treatment or not.

How tDCS works in The brain?

what is exactly happening in the brain during tDCS remains unclear . However, tests on animals, humans, and even direct evidence has been recorded the neurons of the cases tested, ahead lays a general description. the anode (negative) is where the electrons enter the brain. cathode (positive) where the electricity is removed from the brain. thus, when electrons accumulate to enter into a stimulating electrode a negative charge is generated in the stimulating cathode,  (such as passengers waited to board the subway and have the crowd behind).

A smaller cathode can deliver more focal charge to the area in the brain and this is when it gathered more electric charge on the exit door. Therefore, we can form or control the size of the area of the brain, which is affected by changing the cathode electrode size or by changing the size or location of the anode electrode, (Nietzsche et al., 2007).

Behavioral effects of what is happening in the irritating cathode, is not as clear as we wanted to be. In most studies, areas which have been located below the anode , is stimulated and the area where the cathode is located , is inhibited. for example, stimulate different areas of the motor cortex, cause such behavioral effects this method can be used as a treatment for stroke.

However, the brain is very complex. there are studies that show ,Brain's areas follows anode , inhibit in terms of behavioral . In one study, researchers tested latency of recalled visual response: 10 minutes anode's tDCS, cause reduce the scope potential visually stimulated, while 10 minutes the cathode's tDCS , increasing the scope for several minutes after the stimulation.(Akournero et al., 2007). Therefore, in this study , we were  behavior management follows anode, and arousal or stimulation, under the cathode. It seems that different brain areas with morphology, layering and different cell construction , can show different responses to stimulation direct current .

Human head is a poor conductor of addition, lost at least 50 percent of the flow in the peripheral tissues. so that you can use much less electricity, by the time that passes from the skull and directly touches neurons,(Such as DBS or TMS where the magnetic field is passed through the skull).

Scientific rationale tDCS, passing an electric current through the brain using the positive and negative electrodes on the skull. Accordingly, it can be predicted that the important variables to achieve desired effects are including:

  1. Flow: It is natural that the higher the amount of electric current ,will be expected More effects. flow is established from the anode electrode (cathode) to the cathode electrode (anode).
  2. The shape and size of electrode: It can be said  the current density passed through the brain is more important than the intensity of the current,.In fact, the current density represents the flow of every square centimeter. In most studies, can be used 0029 density to 0.08 mA per square centimeter. the shape and size of electrode, will be the decisive indicator . in general, studies have been published using the electrodes 25 to 35 cm , to make a proper connection between the electrodes and skull , use of wet electrode with tap water or a solution of NACl (concentration of 15 to 140 mmol) or especial cream. however, a few manufacturers, have introduced electrodes  without the need for additional material to attach to the skull.
  3. The location of the electrodes: due to the size used and the technical principles of tDCS, can not be expected a large spatial resolution. but regional influence, on the right or left motor cortex or the right or left prefrontal cortex, is possible .research shows that the anode electrode to increase and a cathode electrode leads to reduce the activity of surface area of the cerebral cortex .on this basis we can say that in applying tDCS , in fact, one area of the cerebral cortex is stimulated , and one area is inhibited .
  4. During the flow: it is obvious that the increasing length of flow or rate flow , can be expected more on the effects of tDCS . but considering expanding the scope of affected areas In effect increase rate flow and stimulate the neurons of the lower layers and create uncontrollable effects and evaluation , is preferred to enhance the effect, increase during the period.

during establishment  flow by TDCS in the range of a few seconds , created effects ,immediately destroyed after cutout. in use of tDCS About 10 minutes (General Studies of return of about 9 to 13 minutes use) the effects will remain within an hour.

changes in the excitability of the cerebral cortex by increasing or decreasing the response (irritability) Various methods of electrical stimulation

Type of stimulation

The effect on the excitability of motor cortex cerebral

The cathode tDCS


tDCS anodic


Low-frequency rTMS (less than 1 Hz)


higher-frequency rTMS (equal or more than 5 Hz)


rTMS paired with low-intensity pulse


rTMS paired with high-intensity pulses


TBS row


Intermittent TBS


PAS with low frequency (equal or less than 0.1 Hz)


PAS with low frequency (5 Hz)


TCES pulse


ECS cathode


ECS anodic



ECS: epidural cortical stimulation; PAS: interventional paired associative stimulation; rTMS: repetitive transcranial magnetic stimulation; TBS: theta burst stimulation; TCES: transcutaneous cranial electric stimulation; tDCS: transcranial direct current stimulation.

 Care tips about using tDCS

Due to the use of very mild flow and non-contact electrodes with brain tissue, Several studies have shown that it is completely non-invasive method and without serious complications. The only significant side that some studies have pointed to it , itching and redness in the area where the electrodes after multiple and long meetings the number of patients that the redness and itching not to cause tissue damage But  it mainly caused by vasodilatation flow .

Passing flow from the areas of controlling heart rate or breathing in the brain stem , can theoretically be a study reference electrode was placed in the patient's legs and the other electrodes in the prefrontal cortex. a patient listed report nausea and respiratory problems after the cutout, this problem can be fixed and does not require hospital admission.

Although the use of tDCS in a healthy person cannot be the origin of the creation or increase the possibility of seizure, but the situation may be different in patients with epilepsy. The advantage of this method is not recommended in these patients.  also , patients with unstable situations or with metal objects near the electrodes , don ‘t candidate the use this method. consent form with mention the risk of headache, vertigo, dizziness , nausea should be taken from the patient.  despite the no reported complications in the  studies , It is better, especially in clinical settings and in the long-term protocol, done more carefully, enjoying the examinations and clinical list about patients. side effects of tDCS return the placement of the electrode (cathode or anode) of the stimulation intensity and the length of time that the patient is treated. the older literature have been reported about the treatment of prefrontal that the skin burning can occur,  some patients also feel  undesirable or even dizziness. today treatment ,  ,make the lowest mistake in the worst situation . the group Paulus, reported the results of 576 patients and the challenging studies, upon motor cortex, parietal or occipital, tDCS were received (poyraz et al., 2007). Significantly, no patient did not want to stop stimulation. About 70% of the cases after treatment were fatigue and a third under the electrodes felt the itch. Less commonly reported headache (11%), nausea (3%) and insomnia (1%) as well.

Clinical studies : initial studies suggest that tDCS can enhance certain brain functions independent of the people; However,  technology of tDCS and its application in psychiatry are in the early stages of review. the exist research focuses on the effectiveness of its potential in facilitating recovery from stroke and certain forms of dementia. In a recent unpublished trials double-blind, randomized controlled with the sham (sham is similar Placebo in the treatment like ECT that a patient is connected to a device is turned off) that referred to the journal by Philip Fregny and colleagues, tDCS is used in depression and the results of this study indicate significant effects of antidepressants after anodic polarization in in the prefrontal cortex dorsal - side (DLPFC) . Paulo Sergio Baggio and colleagues in a randomized clinical trial, Double-blind, included 40 patients with major depression, to compare the three groups studied. The highest reduction in symptoms according to measurement Hamilton Depression Scale (HDRS) was observed in the group that Receiving stimulation anode in the DLPFC . the group had about 40% decrease the mark, while a group which was installed occipital electrodes , Showed 21 percent decrease , and the control group had a 10 percent reduction. was observed five full recovery in DLPFC group and in the other two groups was not observed no full recovery .  antidepressant effect remained for a month after the last treatment in the DLPFC group. these findings should be replicated and verified by other centers .

Current status in treatment algorithms: tDCS is not a psychiatric treatment approved by FDA. Hence, is a research and testing technology that needed much work to confirm its effectiveness. if this will  achieve and this instrument will approve by the authorities, tDCS can be inexpensive and relatively safe option in the treatment and an alternative to drugs and have a higher priority than more aggressive stimulation techniques such as ECT or VNS.

Future directions: most current tools of tDCS , use the great electrodes soaked in brine. most likely in the future, will be examine Shape of electrode and contact material  to optimize the  Intended clinical effects and increase ease of their application .However, fundamental questions about the effectiveness, outcomes and dose-response relationships, and also predictors of response are the first grade priority in review .

tDCS compare to ECT:

 The small streams are used in tDCS for more than 20 to 30 minutes. these currents are fixed and your brain has a chance to reconcile with the gentle flow. on the contrary, in the shock therapy (ECT) , use a short, powerful and interactive stream that traditionally, are waveform and makes it like the alternating current.

Your brain can't adapt by stimulating the ECT and cause seizures. the total amount of electricity used at each session of ECT compared with a session of tDCS is not so different. It is known that the brain reacts differently depending on the type of stimulation used and also very different time ranges for each type of stimulation .

The use of tDCS has been used successfully in the treatment of depression (the equivalent of a 6 week period fluoxetine), migraine, pain due to spinal cord trauma And fibromyalgia, stroke, aphasia, craving (drugs, alcohol, cigarettes and food), Parkinson's disease, tinnitus and Alzheimer .  also the plenty of evidence  confirm efficacy of tDCS to improve cognitive abilities such as memory, learning, attention, and planning. . . .