From The Economist:
Electricity has long been used to treat medical disorders. As early as the second century AD, Galen, a Greek physician, recommended the use of electric eels for treating headaches and facial pain. In the 1930s Ugo Cerletti and Lucio Bini, two Italian psychiatrists, used electroconvulsive therapy to treat schizophrenia. These days, such rigorous techniques are practised less widely. But researchers are still investigating how a gentler electric therapy appears to treat depression.
Vagus-nerve stimulation, to give it its proper name, was originally developed to treat severe epilepsy. It requires a pacemaker-like device to be implanted in a patient’s chest and wires from it threaded up to the vagus nerve on the left side of his neck. In the normal course of events, this provides an electrical pulse to the vagus nerve for 30 seconds every five minutes.
This treatment does not always work, but in some cases where it failed (the number of epileptic seizures experienced by a patient remaining the same), that patient nevertheless reported feeling much better after receiving the implant. This secondary effect led to trials for treating depression and, in 2005, America’s Food and Drug Administration approved the therapy for depression that fails to respond to all conventional treatments, including drugs and psychotherapy.