In the distant past, people applied electrical stimulation to treat patients by using electric catfish. Recently, transcranial direct current stimulation (tDCS) has attracted more and more interest. The basic design of this technique was made one hundred years ago. It was rediscovered in the early 2000s, and has been increasingly studied since then.
The use of electrical stimulation to treat diseases has a long history. The ancient Egyptians used electric catfish out of the Nile to stimulate themselves to treat certain nervous diseases.
The Roman physician Scribonius Largus treated a patient with gout by using a live torpedo fish. He wrote that headaches and other pains could be cured by standing in shallow water near these electric fish in 46 AD.
Ibn Sidah was a Muslim doctor of the eleventh century. He believed that a live electric catfish had beneficial effects when placed on the brow of a person suffering an epileptic seizure. The recipes for the torpedo and its ilk have been cited until the end of the renaissance.
By the time of 1930s, electroconvulsive/electroshock therapy (ECT) emerged. Ugo Cerletti, the Italian psychiatrist, who in 1938 came up with the idea for treating human beings with electroshock therapy. Cerletti observed that pigs were electrocuted into unconsciousness as a kind of anesthesia to make the process of slaughter easier. He concluded that this method could be useful to patients with mental illness. Not more than a year after Cerletti got his brilliant idea, it was introduced into the United States.
For the next thirty years, hundred of thousands of patients of all ages, received electroshock treatments for every type of mental disorders. But by the end of the 1960s, ECT had almost disappeared from the psychiatric scene, due to the use of more effective neuroleptics and an anti-ECT movement. This cessation was motivated by the numerous side-effects of ECT, such as memory loss.
In the 1960s, there was an increased interest in tDCS (transcranial direct current stimulation). A series of studies were published in the 1960s and 1970s. It was proven that tDCS could affect brain function by changing the cortical excitability (the rate at which neurons fire). Animal experiments showed that neuronal activity could be changed immediately and this could last for several hours. These studies marked the beginning of tDCS.
However, there were still many fundamental unsolved questions such as the stimulation current densities. These questions caused inconsistent results in human experiments. Meanwhile, drug therapy had become a very profitable method of therapy. As a result, this intervention was not persuasive enough to be adopted by clinicians. And soon it was very much abandoned.
It was not until the early 2000s, the interest in tDCS was revived. Nitsche and his colleagues at the university of Gottingen in Germany rediscovered the technique and carried out a series of studies. From then on, hundreds of tDCS studies have been done in the next decades. This was aided by the significant advances in new brain imaging techniques.
From 2000 to November 2012, more than 500 tDCS studies were completed. This occupies approximately three quarters of the total number of studies ever published. The studies researched on brain function and possible therapies for stroke, pain, depression, motor and psychiatric concerns.
Nitsche and his colleagues offered an overview in their 2008 article: the state of the art of tDCS. It is a very comprehensive guide to the current state of research on tDCS. They summarized effects of different stimulation electrode positions with varied physical parameters. This paper was published in the July 2008 issue of Brain Stimulation.
Just as this paper points out, the study of tDCS is still in its early stages but advancing rapidly. Many institutions have only recently started to investigate this technique, as a promising tool in human neuroscience research and for potential treatments.
A more in-depth history of Transcranial Electro Stimulation with proper references can be read here.