Stone tablets dating from Ancient Egypt (2,500 years B.C.) have been found on which a technique to relieve pain using an electric fish was depicted.
At the time of Socrates, arthritis pain and headaches were also treated this way. It is only in 1965 that Ronald Melzack (psychologist) and Patrick Wall (physiologist) systematized the technique and gave it its name: Transcutaneous electric nerve stimulation.
Today, this technique is widely used in hospitals and clinics to relieve different types of pain, usually in combination with other physical or medicated treatments.
Two main hypotheses currently exist to explain the analgesic action of the TENS : the gate control theory and the stimulation of the natural analgesic endogenous production.
According to the gate control theory, the electric current sent to the nerves contributes to block the passage of pain information to the brain. This would close the gateway between the nerves and the spinal cord, normal transmission route for nerve impulses to the thalamus and cerebral cortex.
The endogenous analgesics are analgesic substances produced naturally by the body according to its needs. They include the endorphins, enkephalins and dynorphins, morphine-related substances. Their production would therefore be stimulated by the passage of electric current in the nerves.
It is also possible that the analgesic effects of the transcutaneous neurostimulation (TENS) are the result of those two mechanisms. In any case, transcutaneous neurostimulation (TENS.) is often used to relieve different types of pain.