The vagus nerve, or cranial nerve X, is a part of the autonomic nervous system, which controls functions of the body that are not under voluntary control, such as heart rate and digestion. In the neck, the vagus nerve travels near the carotid artery and jugular vein.

Interestingly, neurologists in the 19th century noted that applying pressure on the carotid artery in the neck, and thus the vagus nerve, could stop seizures. Recent research found that stimulation of the vagus nerve in animals decreases both epileptic activity in the EEG and the frequency and severity of seizures. After proven seizure reduction in animals using VNS, several controlled human trials demonstrated a significant reduction in seizures with minimal side effects.

In 1997, the FDA approved vagus nerve stimulation in patients older than 12 with refractory partial epilepsy. Mounting clinical experience also demonstrates efficacy and safety in children and in patients with generalized epilepsies.