ECT is a treatment for a small number of severe mental illnesses. It was developed in the 1930s and was used widely during the 1950s and 1960s for a variety of conditions. It is now only used for fewer, more serious conditions.
An electrical current is passed through the brain to produce an epileptic fit – hence the name, electro-convulsive. On the face of it, this sounds odd. The idea developed in the days before effective medication. Doctors noticed that some people with depression or schizophrenia, who also had epilepsy, seemed to feel better after having a fit.
More recent research suggests that the effect is due to the fit rather than the electrical current.