Vagus nerve stimulation (VNS) is a treatment method to stimulate the vagus nerve using a surgically implanted small electrical device (similar to a pacemaker). VNS has been approved by the Food and Drug Administration (FDA) to treat epilepsy characterized and certain cases of severe, chronic depression. VNS is used in addition to seizure medications.

The therapy has been shown to reduce seizures in some people with epilepsy by approximately 20 to 40 percent, according to the National Institutes of Health (NIH). VNS is not a cure for epilepsy, its use is meant for cases that do not respond to medication or brain surgery. The effect of VNS on depression is less clear. More studies are necessary to determine what impact VNS may have for the treatment of depression. Roughly 32,000 people have the vagus nerve stimulation device implanted, most of of them implanted for the treatment of epilepsy, according to the Epilepsy Foundation.

The vagus nerve is one of the most important nerves in the body. It is a paired nerve that runs down each side of the spinal cord from the brainstem to the abdomen, passing through numerous organs and transmitting information from these organs to the brain. The vagus nerve controls functions such as heartbeat, gag reflex and digestion. It is also thought that the vagus nerve is associated in some way with serotonin, a chemical in the brain responsible for controlling mood, sleep and appetite.

A vagus nerve stimulator is a small battery-like device with silicone-coated electrodes attached, measuring about 2 inches (5 centimeters) diameter. The stimulator is inserted into the left side of the chest and the electrodes are placed around the vagus nerve in the neck. When the stimulator is turned on, it sends small pulses of electricity through the electrodes and into the vagus nerve at regular intervals (e.g., 30 seconds of stimulation every five minutes), 24 hours a day.

Patients are given a magnet, which they can use to turn the device on or off. The magnet can be worn like a watch or a belt. It can also be used to deliver stimulation in between the normal intervals. This is especially useful for those able to sense when their seizures are about to occur.

The batteries of the stimulator usually require replacement every six years. The device itself may last up to 12 years, according to the manufacturer.

Much like other epilepsy treatments, it is unclear exactly how VNS works to control seizures or reduce depression. Stimulating the vagus nerve may increase blood flow to several parts of the brain that may play a role in seizure activity and mood.

VNS was first approved for treatment of generalized seizures. It is now believed that vagus nerve stimulation can be used to treat numerous types of seizures and research is being conducted into other possible uses.  

Side effects are usually mild and decrease over time. Many people experience a change of voice tone during stimulation because the vagus nerve controls many aspects of vocal function. For this reason, vagus nerve stimulation may not be suitable for people who rely on their voices, such as singers or public speakers.