The vagus nerve is the tenth of the twelve pairs of cranial nerves that arise from the brain. Its name comes from the Latin word for "wandering." The name fits. The nerve leaves the brainstem, travels down the neck, and reaches the organs of the chest and abdomen. It sends branches to the heart, the lungs, and the digestive tract.
The vagus is mostly known as the nerve that slows the heart rate and regulates digestion. However, its fibers do not only carry information from the brain to the organs. About eighty percent of its fibers work in the opposite direction and carry information from the organs to the brain. This information first reaches the solitary nucleus in the brainstem. From there, it spreads to wide areas of the brain.
Vagus nerve stimulation uses this pathway. A low-intensity electrical current is delivered to the vagus nerve at regular intervals. The signal travels upward from the brainstem and regulates electrical activity in the brain.
The first attempt came in the 1880s, when the New York neurologist James Leonard Corning tried to prevent seizures by applying pressure and electricity to the vessels and nerves of the neck. In the 1980s, Jacob Zabara showed that vagus nerve stimulation stopped seizures in dogs. The first vagus nerve stimulation device was implanted in a human in 1988. The method was approved for the treatment of epilepsy in Europe in 1994 and in the United States in 1997.
Today, the most common use of vagus nerve stimulation is drug-resistant epilepsy. In about two-thirds of people with epilepsy, seizures are controlled with medication. In the rest, seizures continue despite two appropriately chosen medications used at adequate doses. This is called drug-resistant epilepsy. Vagus nerve stimulation is an important option for patients who are not candidates for surgery or who do not benefit enough from surgery. It is used in both focal and generalized epilepsies. It is also used in children. It has a role in severe childhood epilepsies such as Lennox-Gastaut syndrome.
The device has two parts. A pulse generator smaller than a pocket watch is placed under the skin below the left collarbone. A thin electrode is wrapped around the left vagus nerve in the neck. The left side is preferred because the right vagus sends more fibers to the heart's pacemaker. The procedure usually takes about an hour. Most patients go home the same day or the next day.
The current is started at a low level. The physician increases it step by step at follow-up visits. Programming is done wirelessly. Stimulation is delivered in cycles, for example thirty seconds on and five minutes off. The patient or a family member can trigger extra stimulation by passing a magnet over the device. When given at the start of a seizure, this stimulation shortens or stops the seizure in some patients. Newer devices detect the sudden rise in heart rate during a seizure and deliver extra stimulation automatically.
Vagus nerve stimulation rarely eliminates seizures completely. The goal is to reduce seizure frequency and severity. In long-term follow-up, seizure frequency falls by half or more in about half of patients. Few patients become completely seizure-free. The effect does not appear immediately. It grows over months. The clearest benefit is often seen after the first or second year. Seizures may become shorter. Recovery after a seizure may become easier. Falls that cause injury may decrease. Many patients report improvement in alertness, mood, and quality of life.
Side effects mostly occur during stimulation. The most common are hoarseness and changes in the voice. Coughing, a feeling of tightness in the throat, and shortness of breath may occur. These are usually mild, fade over time, and can be relieved by adjusting the current.
The battery lasts several years, depending on the settings. Before it runs out, the generator is replaced with a minor procedure, and the electrode stays in place. MRI is possible, but only under certain conditions. Before the scan, the device must be set to the appropriate mode and specific scanning rules must be followed. Whenever an MRI is planned, the center following the patient should be informed.
The use of the method is not limited to epilepsy. Improvement in mood among patients with epilepsy led researchers to study depression. Vagus nerve stimulation was approved in the United States for treatment-resistant depression in 2005. In 2021, a system that delivers stimulation paired with rehabilitation exercises was approved to improve arm function after stroke. The effect of the vagus nerve on the immune system has also been studied in inflammatory diseases such as rheumatoid arthritis. Devices that stimulate through the skin of the neck or the outer ear, without surgery, have also been developed. Devices applied to the neck have been tried in migraine and cluster headache. The role of ear-based stimulation in epilepsy is not yet clear.
References Kwan P, et al. Definition of drug resistant epilepsy: consensus proposal by the ad hoc Task Force of the ILAE Commission on Therapeutic Strategies. Epilepsia 2010;51:1069-1077. Englot DJ, et al. Vagus nerve stimulation for epilepsy: a meta-analysis of efficacy and predictors of response. J Neurosurg 2011;115:1248-1255. Morris GL 3rd, et al. Evidence-based guideline update: vagus nerve stimulation for the treatment of epilepsy. Neurology 2013;81:1453-1459.
