History:

The initial design of tDCS electrical brain stimulation dates back more than 100 years. A number of early experiments using this technique were conducted on animal and human samples before the 19th century. Luigi Galvani and Alessandro Volta were two researchers who used this technology to identify the source of electricity in animal cells. In 1804, Aldini began a study on the application of tDCS electrical brain stimulation, which was effective in improving the mood of depressed people.

In the 1960s, a person named Albert was able to show that tDCS affects brain function by changing the excitability of the cerebral cortex. He also discovered that positive and negative stimulation have different effects on cortical excitability. Although these findings were important for the clinical use of tDCS, given the paucity of research in this area, pharmacotherapy has shown itself to be a more effective method of treatment.

This argument continued until the present day, until with the increased interest in studies regarding the basic functions of the brain and therapeutic applications, this method was revived as new brain stimulation methods such as magnetic brain stimulation (TMS) and new brain imaging techniques such as functional fMRI imaging.

The working principle is that two electrodes, one positive pole and the other negative pole, are placed on the head through a sponge pad that is wetted with a conductive solution. After passing through different areas (scalp, skull, etc.), the electric current by these electrodes reaches the surface of the cerebral cortex. The current that reaches this area gives the neurons an electric charge and creates a positive and negative pole, which leads to a change in the activity of that area.

According to the disorder that exists in performing this method, the following must be specified:

• The intensity of electric current, its duration and direction
• The location of each electrode
• The size of the sponge pads used
• Number of sessions

After some time since tDCS became popular, a new approach was introduced in which instead of using two pads, a number of electrodes of smaller sizes are used to target specific cortical structures. This approach is known as high-definition tDCS (HD-tDCS). In a preliminary study, it was found that HD-tDCS has more and longer changes in the excitability of the motor cortex than the conventional method.

Types of stimulation:

There are three types of electrical stimulation of the brain: positive (anodal), negative (cathodal) and sham (sham). In positive or anodal stimulation, the nervous excitability of the target area increases; However, in negative stimulation, the opposite of this problem occurs. The sham condition is also used for the control group in the studies. In this case, a short stimulation takes place and then it stops. In this case, the person does not realize how long the stimulation has been on him. It is due to the existence of this state that researchers can determine the real effect of this method compared to the effect of suggestion or placebo.

One of the most important dimensions of this method is its ability to achieve the changes made in the cerebral cortex even after the end of the stimulation. The duration of these changes depends on the duration of stimulation as well as the intensity of stimulation. The function of the brain changes according to the depolarization or hyperpolarization that happened in the resting potential of the membrane.

applications:

tDCS electrical brain stimulation has been used in the treatment of disorders such as depression, migraines, post-stroke rehabilitation, addiction cravings, tinnitus, Parkinson’s, chronic pain, anxiety disorders and schizophrenia. Also, tests on healthy people have shown that this method can increase their cognitive performance depending on the area that is stimulated, such as speech and math abilities, attention span, memory, etc.

Risks and side effects:

So far, no risks have been reported regarding the use of this method. But since tDCS is a stimulation method, precautions must be taken. Including the use of the correct protocol and its correct implementation, as well as recommending more caution in people prone to seizures such as epilepsy.

There are also minor side effects that can occur during stimulation. These side effects include: skin burning, phosphene phenomenon (seeing white lights) at the beginning of stimulation, nausea, headache, dizziness and itching under the electrode. In a study where a protocol was implemented on 500 people, only a mild skin irritation and a phosphene were reported as side effects.

Among the non-invasive methods in the treatment of various psychiatric, neurological and psychological disorders, rTMS magnetic brain stimulation, neurofeedback and biofeedback can also be mentioned.