Transcranial direct current stimulation or TDCS is a relatively new technique being used in the treatment of autism spectrum disorder (ASD). However, precedents for the TDCS machine and its use can be found dating back to the mid 1800’s. It is therefore noteworthy that despite its recent popularity, historical evidence suggests that electrotherapeutic interventions with TDCS-like devices were ineffective, offering little or no therapeutic value besides placebo. In this blog, I will provide a historical background to TDCS-like devices. Those interested in reading a criticism about the therapeutic claims of TDCS can access a previous blog that I wrote for corticalchauvinism.com (TDCS and autism: beneficial intervention or quack therapy?).
Archeological digs of ancient Roman sites have uncovered pots inlaid with copper that could have stored electric charge in a way similar as to how modern capacitors work (see Leyden jar). However, it was not until the 17th century, with the invention of the electrostatic generator and classification of materials as conductors and insulators, that scientists regarded electricity as a main area of study. In 1800, Alessandro Volta described how closely apposed discs of zinc and copper, wrapped with a brine-soaked substance, produced electricity. Piling discs upon themselves had an additive effect on voltage that made the contraption act as a primitive power source or battery. The voltaic pile was a source of continuous electricity that did not change polarity. Over time this source of direct current was called galvanic; but, when interrupted and pulsed, the current was called faradic. The new modality of pulsed electric current was considered a significant innovation as it was more effective in eliciting muscle contractions. The large majority of electrical shock devices provided means for both galvanic and faradic stimulation.
Medical instruments based on static electricity (so-called frictional machines) were seldom mass produced. It did not help that they were also large, bulky, and expensive. In addition, credence as to their therapeutic effectiveness was disputed. Some people believed that despite the high voltage produced by frictional machines, the extremely low currents (.2 to 3 mA) were not enough to penetrate the skin. To distinguish frictional machines from other galvanic and faradic output devices those based on static current were called Franklinic. (Note: modern TDCS equipment usually operates with a 9V battery and generate 0.5 to 2 Amp at maximum power. In the mid 1800’s, a prominent maker of electrotherapeutic devices, published his Manual of Magnetism. In this manual, Davis doubted whether such minute currents could pass through the skin and have a significant effect on organs of the body [Licht, 1959]).
In 1883, an American medical doctor, nutritionist and inventor by the name of John Harvey Kellog (1852-1943) introduced the use of sinusoidal current into medicine. It is surprising that the most enduring legacy of Dr. Kellog came later on in 1894 while being the Direct of the Battle Creek Sanitarium. In that year Dr. Kellog introduced corn flakes as a nutritious breakfast cereal. Dr. Kellog, the original wellness guru, converted his Sanitarium into a holistic church grounded on dietary and electrophysiological interventions.
The smoother and more symmetrical sinusoidal current introduced by Dr. Kellog was better tolerated than the pulsed current of faradic devices. Dr. Kellog claimed that the application of sinusoidal current had benefits for lead poisoning, tuberculosis, obesity and, when applied directly over the eyeballs, a variety of vision disorders. Unfortunately, the use of the new equipment was limited as it required a motor powered-up by an electrical outlet. The new therapy could only be administered by a physician and was not available for in-home use by patients.
Until the invention of the telegraph and the telephone there was no commercial utility for electricity. The use of electrical shock devices was therefore relegated to medical and scientific institutions. By 1880 medical demand was high enough for small factories or manufacturing shops of electroshock devices to appear throughout Europe and the United States. These devices were known by many names including, medical electrical batteries, electrical stimulators, quack boxes, and shock machines. In present times, these machines include transcranial direct current stimulation devices (TDCS) and transcutaneous electrical nerve stimulator (TENS) units. The introduction of X-ray machines in the late 1890’s changed the direction of medical research and diminished the demand for electroshock devices. Thereafter, medical electrical stimulators were almost abandoned by physicians and became part of the therapeutic armamentarium of physical therapists.
Throughout the years, technology has changed the equipment to make the devices smaller, more portable, and to offer better safeguards to the patients (e.g., offering a constant source of electricity, controlling the electrical output). The way they work, if they do, remains a mystery. Early physicians believed that electricity served to transfer energy to the body, thus strengthening the “force of life”. It was therefore considered of special use in treating “weakness of the nerves” or neuroasthenia (i.e., a combination of weakness, lack of concentration and depression). At present the use of TDCS is being explored for, among many other conditions, depression, schizophrenia, aphasia, addiction, epilepsy, chronic pain, attention, and motor rehabilitation. The claims of TDCS as a cure-all should raise a red flag to both medical professionals and patients.
Over the years I have been able to collect a number of early electrotherapeutic devices. Several pieces of my collection are shown below.
The Branstom Medical batteries were manufactured in Toronto, Canada. Their instruction booklet (see above) for treatment with Faradic and Galvanic current claimed beneficial effects for asthma, catalepsy, catarrh, chlorosis (iron deficiency anemia), constipation, convulsions, cramps, dyspepsia, gout, headache, hip joint disease, hysteria, lameness, nervous exhaustion, rheumatism, sprains, and toothache. In similar fashion, TDCS is offered as a medical panacea in modern times.
A variety of electrodes allowed the physician to apply the current in different areas of the body. A pin holder electrode antedated modern electric acupuncture. Some electrodes were adapted for the hair (brushes), rectum, and to be strapped to the wrist.
An early medical battery meant to provide direct current at varying voltages.
A “magneto-electric machine” dating to the 1850’s. The superb workmanship is exemplified by the use of brass gears and pulley drive. A hand crank turned two coils at great speed against a magnet. The device was produced individually by the Pike family (Boston) of opticians. The Pike family went to expand their production to include barometers and surveyor’s equipment.
Like other quality surgical instruments many of the knobs in this device were plated to resist corrosion and make it more appealing. The faceplate is made of a dull black solid material. Bakelite was introduce many decades after this machine was produced, making me believe that this particular faceplate was made from gutta percha. This would make sense as gutta percha acts as an insulator to all of the current carrying wires directly below. (Note: faceplates made of wood were often carved underneath for wires thus resembling the original breadboards used in electrical circuits). A couple of interrupters are noted. These interrupters acted to provide “faradic” (pulsed DC current) and a reassuring buzzing sound for the patient. The voltage was controlled by the on switch which selected the number of batteries in series that would power the device. Many of these devices were imported to the United States where a brand plate would be added.
Higher voltage were provided by induction coils (think solenoid of a car). The coils were often covered in fabric. A secondary insulated coil was wrapped on top of the primary. A sliding bar placed inside of the coil acted as the core. Keeping the bar inside the coil concentrated the flux lines at its center, thus diminishing the inductive phenomena and keeping the voltage at a low level. The presence of interrupters acted to provide a pulsed DC current. Adjusting the interruptors with a screw changed the frequency of the pulses. The resultant pulsed wave did not have major inductive spikes, given the low frequency of the pulses.
Let me conclude by saying that, ” …it is believed that they [electrotherapeutic machines] were forced off of the market by the AMA during the 1930’s because medical professionals found that drugs were more profitable. Doctors who used electricity for any health problem were threatened with being called a quack and loosing their medical license”. (from: http://medical-electric-battery.com/)
Casanova MF. Autism Updated: Symptoms, Treatments and Controversies. Amazon Publishing, 2019.
Licht S (ed). Electricity and ultraviolet radiation. New Haven, CT, Elizabeth Licht Pub, 1959.