The use of electricity to provide analgesia is not new. The first use of such treatment involved “electric” fish. Nile catfish decorations appear on Egyptian tombs from the 5th Dynasty, 2750 BC. Greek literature reports the use of the torpedo ray. Aristotle wrote that “the torpedo fish can produce numbness, even in humans”. In fact, the word “torpedo” comes from the Latin “torpere” meaning numb.

The emergence of electrical treatment can be dated from a historical event that occurred under the reign of the Emperor Tiberius, in 36 AD. After freeing his favourite slave Anteros, Tiberius met with him and the following dialogue is reported: “Tell me, Anteros, you are not limping today? No, Devine Emperor, and I am myself surprised…And the gout in your foot? Disappeared, Divine Emperor…What do you mean? Tell me!” Anteros replies: “This morning I was walking on the beach when my foot touched a beached torpedo fish which had landed on the shore not much earlier. Ah! By Jupiter, what a shock! It felt like a bolt of lightning, then nothing… Nervously, I continued my walk and, Ô surprise; my gout pain had completely disappeared. I now walk with no pain when I could not make one step without suffering”.

Scribonius Largus, a doctor in Rome, heard about this healing. He later became the personal doctor of Emperor Claudius, who succeeded Tiberius (and Caligula). Here is a typical prescription by Scribonius Largus: “For all gout pain, the foot should be placed on a live black torpedo fish. The patient should remain on a damp sea shore until his foot and leg are numb to the knee”. This treatment was prescribed to Emperor Claudius for gout and headaches.

During his colossal work (300 to 600 books), Galen (131–201 BC) studied electric fish, both live and dead. He reported that eating the fish provided no pain relief, but the application of a live fish, which gave an electric shock, was an effective analgesic. Galen’s work influenced medicine for 1500 years. More recently, “electric” fish have been found to produce discharges of 40 to 50 volts.

Two thousand years later, questions remain about the use of electricity for analgesia: Can (painful) electrical stimulation reduce pain? and Which mechanisms and nerve pathways are involved in the effect?

It is certain that the “gate control” theory, based on the transmission of non-painful signals by large-diameter fibres, cannot explain the antalgesic effect of electrical stimulation by torpedo fish. This question was investigated by Roby-Brami et al. in healthy subjects (including the authors) and patients with American Spinal Injury Association (ASIA) A tetraplegia (complete) above C5, at Raymond-Poincaré hospital, Garches, France. The test pain was provoked by electrical stimulation of the sural nerve (a sequence of 8.1 ms pulses for 30 ms) every 15 s. In healthy subjects, this stimulation generated pain associated with a polysynaptic reflex in the tibialis anterior muscle. Healthy subjects perceived and could rate this pain on a visual analog scale (0–10). Moreover, the level of pain was perfectly correlated with the intensity of the stimulation (measured in milliamps). The polysynaptic response increased in parallel.

In healthy subjects when a painful stimulation (long-duration electrical stimulation of the ulnar nerve or a pinching force) is applied to another part of the body (upper limb or face), the stimulation of the sural nerve is perceived as less painful and the polysynaptic tibialis anterior reflex is greatly reduced ( Fig. 1 A). This dual effect on pain and the lumbar polysynaptic reflex shows that the effect depends on pathways from the brainstem and/or propriospinal pathways from the cervical to lumbar sections of the spinal cord. These pathways inhibit the pain pathways and the flexion reflex in parallel, so the inhibition affects a neuron that is common to both pain sensation and the flexion reflex. More precisely, it probably inhibits the first spinal interneuron that is activated by nociceptive afferents, which is also the first of 3 interneurons that cause the flexion reflex.

Example of the effects of heterotopic nociceptive stimulation of the RIII reflex in a normal subject (A) and tetraplegic patient (B). Each trace represents the mean of 10 responses recorded within 1 min. The conditioning period is indicated by arrows.

Patients with ASIA A tetraplegia above C5 do not perceive any pain from the electrical stimulation of the upper or lower limbs. However, the “nociceptive” stimulation of the lower limb generates a flexion reflex. Stimulation of “nociceptive” intensity of an upper limb does not generate a perception of pain, but it activates afferents that transmit the nociceptive message to the spinal cord and could activate the propriospinal tracts.

In contrast with healthy subjects, in tetraplegic patients, the stimulation does not reduce the polysynaptic reflex ( Fig. 1 B). This is a strong argument demonstrating that the pathways activated by nociceptive afferents, which inhibit another nociceptive message and a “nociceptive” spinal reflex pass via a structure in the brainstem. In patients with high-level tetraplegia, the propriospinal tracts that unite the brachial and lumbosacral regions are normal and should be able to reduce the lumbar polysynaptic reflex.

Could this explain the findings of the ancient Romans? Yes: one nociceptive stimulation can mask another. However, the effect we obtained (in healthy subjects) is temporary (lasting only several minutes after the end of the upper limb stimulation [ Fig. 1 A]) and does not explain how pain could be relieved for several days. However, the “analgesic pain” used in the Roby-Brami et al. study was of lower intensity than that used to treat Emperor Claudius.

Little emerged during the middle ages and the renaissance period.

In 1745, Pieter van Musschenbroek, a professor at the University of Leyde, described an experiment with electrified water contained in a bottle. He received a shock during the experiment that was so violent he thought “it was all over” for him. From this was born the “Leyden jar”, the first condenser to stock electricity, thus facilitating its use in medicine.

Jean Jallabert, a professor of physics in Geneva, was a corresponding member of the Paris Academy of Science and the Royal Society of London before becoming President of the Geneva republic. In 1748, he published a report of a locksmith named Nogues with right hemiplegia after a trauma 5 years previously, who was healed by the application of static electricity . Jallabert directed the electrical current to the extensor muscles of the forearm and found a notable improvement in movement. After treating the patient throughout the year 1747, Jallabert announced the cure. News of this publication spread considerably.

This news was followed by a considerable number of publications of cures or improvements in different types of muscle hypertonia. In France, the priest Abbé Nollet developed a machine to generate static electricity: a glass sphere coated in pulverised wax that turned by means of a cutler’s wheel. The electrical spark produced by the rubbing of the moving sphere was then collected and conducted to the patient via a metal circuit. Many therapists became illustrious, including a researcher who is more famous for his political notoriety: JP Marat. Marat proposed to treat and cure many neurological conditions such as hemiplegia and sciatica…but not venereal disease.

However, even the most enthusiastic therapists had some criticisms. Abbé Nollet wrote on the subject of some “cures” that mostly occur in poor people who know that they will be helped if they can draw attention to themselves…. Benjamin Franklin expressed similar scepticism at the end of his Research on Electricity . While he was American ambassador to France, he wrote on the subject of these treatments that “the sight of a machine or an unexpected effect could have such a singular effect on the soul that it would alter the state and disposition of the body.” It appears that the inventor of the lightning rod also invented the placebo effect.

Two new facts appeared at the end of the 18th century:

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  Galvani, professor of anatomy in Bologna in 1781, had put several frogs to dry on his balcony (to make a soup for his wife who was “suffering”). On the table near the frogs was an electrical machine . When a student mechanically moved the point of a scalpel close to one of the frogs, strong convulsions immediately occurred in all muscles of its limb;

  
  
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  in 1800, Volta perfected the voltaic pile, which he presented to the Academy of Science in 1801 in the presence of Napoleon (who was King of Italy at the time).

The invention of the voltaic pile meant that electrical currents could be used more easily. Volta maintained that the contractions in the muscles of the frog were produced by contact from two different metals, thus generating a current that was not produced by the animal.

A student and nephew of Galvani, Giovanni Aldini, travelled the world to demonstrate the benefits of electricity on the human body . He carried out public experiments on cadavers of animals and prisoners who had recently been decapitated or hung, demonstrating that the application of electricity to the head caused certain muscles to contract. The most famous of these experiments, on January 7, 1803, was on the body of the prisoner George Foster in the presence of the Royal College of Surgeons in London.

Electrical stimulation became a common treatment for neurological and psychiatric disorders (1804), and detailed observations may still be consulted. Aldini specified that his method was more particularly indicated for the treatment of melancholy.

Of these numerous descriptions of the effects of electricity throughout the 19th century, the work of Duchenne de Boulogne is particularly notable. A general practitioner in his hometown of Boulogne, he had a passion for medicine, photography and electricity. He treated his patients with electro-acupuncture. He used a technique developed by Faraday, which allowed for modulating the duration and intensity of the currents generated, so it was more controllable and less dangerous than previous techniques. Using this technique, Duchenne was able to stimulate a single muscle fibre very precisely, either directly or by stimulating the nerve. He then meticulously identified all the resulting facial expressions. Moreover, with a little harpoon he had invented and remembering his patients from Boulogne, he performed well-localised biopsies. He described and specified the muscle lesions that occurred in the myopathy to which his name is attributed. He was considered a master by Jean-Martin Charcot, who helped him describe different afflictions, including amyotrophic lateral sclerosis. Under this impetus, Charcot created the electrology department at Salpêtrière Hospital.

Treatment by electrical stimulation was fashionable at the end of the 19th and beginning of the 20th centuries. As well as stimulation for treating neurological and psychiatric disorders, short-wave ultrasound diathermy was developed for many applications following the work of Jacques-Arsène d’Arsonval . However, little development remains, except, perhaps, the electric scalpel. At this time, a medical speciality termed electroradiography had been developed, and some physicians (and particularly paramedical professionals) were more like “electricians” than radiologists.

When I arrived as a young doctor in the rehabilitation department run by Mr. Held at Salpêtrière hospital in May 1968, the wife of Mr. Held’s predecessor worked as an electro-radiologist. She prescribed a particular treatment for spasticity and motor impairment following cerebral lesions called “transcerebral spinal ionisation”. This treatment had some similarities with transcranial direct current stimulation used today. A continuous current was applied with the anode on the ocular globe and the cathode over the occiput. The sponges were instilled with a Ca or Mg solution. This technique was reputed to inhibit spasticity by the inhibitory effect of the Ca or Mg ions on the brainstem.

Today, new studies that appear daily in PubMed boast of the almost “magical” effects of non-invasive electrical stimulations! Are we replaying the history of the 18th century? What lessons can we learn from history? Maybe we should cast a critical eye as Benjamin Franklin did. Moreover, we now have greater knowledge of anatomy and physiology, and, especially, many methods exist to quantify the effects of treatments.