Oftentimes, neural-based conditions can be treated effectively with prescription medications or even some forms of counseling. However, doctors and researchers have also found that stimulation of the vagus nerve, using electrical impulses, can have beneficial results in treating a number of ailments.
The vagus nerve -- among the longest, most complex and most important nerves in the human body -- takes its name from the Latin word for "wandering." And for good reason. One of 12 pairs of cranial nerves responsible for the body's involuntary motor and sensory functions, the vagus nerve is also known as the 10th cranial nerve, and it connects the brain stem (at the medulla oblongata) to the abdomen -- while branching out to form a complex circuit that links our gray matter to our larynx, heart, lungs and gastrointestinal tract, including the stomach and colon.
The twin sets of nerves that make up the vagus pass through the neck as they meander between the chest and midsection and the lower part of the brain. These nerves are responsible for a number of bodily functions, including motor functions in the voice box, diaphragm, stomach and heart, and sensory functions in the ears and tongue [source: AANS]. The nerve is also connected to both motor and sensory functions in the sinuses and esophagus. As a result, damage to the vagus nerve, either through trauma or congenital causes, can have an impact on those functions.
In treating depression, potential patients must meet fairly strict criteria to be considered for vagus nerve stimulation (VNS). Candidates must be at least 18 years old, have been diagnosed with treatment-resistant depression, have suffered from chronic depression for more than two years, and have not seen any improvement in their condition through the use of antidepressants or ECT, also known as electroconvulsive therapy [sources Tracy; Mayo Clinic].
What are the major functions of the vagus nerve?
Functions of the Vagus Nerve
The vagus nerve has the most extensive distribution of all the cranial nerves. It's actually two nerves, which both run from the brain stem and branch out through the neck and down each side of the body, across the abdomen and to the main organs.
As a result, the remarkably complex circuitry that makes up the entire vagus nerve has a role in myriad bodily functions, including breathing, maintaining digestive function, and monitoring the heart beat to keep it in a regular rhythm. When we're hungry or feel our chest tighten, it's the vagus nerve relaying that message. The vagus nerve also relays sensory information from the ear, tongue, throat, windpipe and voice box.
Like the nerve itself, vagus nerve disorders are often also called 10th cranial nerve disorders. These disorders can have a variety of different impacts that are as complex as the nerve itself, though some effects are more common than others.
For example, if the vagus nerve is stimulated, or if it is compressed, the result is usually clammy, cool skin, unconsciousness, and/or nausea. This is because when stimulated, the vagus nerve causes the heart to slow down and blood pressure levels to drop. While this might appear to be detrimental in many cases, the vagus nerve is sometimes stimulated to treat people suffering from severe depression or epilepsy [source: Tian].
What is vagus nerve stimulation?
About Vagus Nerve Stimulation
Vagus nerve stimulation (VNS) is a procedure in which a pacemaker-like device is implanted underneath the skin in the chest to literally stimulate the nerve. The nerve is enlivened by mild electrical impulses, which can interrupt or suppress abnormal activity and restore the standard neural pathway to the brain. The impulses are also believed to have an affect on the brain's so-called mood centers [source: Mayo Clinic].
According to the American Association of Neurological surgeons (AANS), the typical surgery to implant a pulse generator runs about an hour to 90 minutes and is performed under general anesthesia (patients with any known allergies should apprise the anesthesiologist). However, with improvements in surgical techniques, it's becoming more common to have this operation done under local anesthesia on an outpatient basis, therefore avoiding an expensive overnight hospital stay.
The pulse generator itself is a flat, round piece of metal about the size of a silver dollar, measuring roughly 1.5 inches (3.8 centimeters) wide and 0.47 inches (12 millimeters) thick, though newer models are getting smaller all the time. This battery-run device (see sidebar) emits the impulses that stimulate the nerve's circuitry. The duration of these impulses is set by the surgeon via a programming wand, typically two weeks to a month following surgery, and can be adjusted during future visits. Further, patients (and/or caregivers) can temporarily adjust the impulses by using a handheld magnet.
As with any surgery that requires incisions, there is always a small risk of infection (bringing to mind the old maxim, "The only minor surgery is the surgery that is happening on someone else"). Surgeons must also take special care not to damage the nerve itself or the surrounding blood vessels, including the carotid artery and jugular vein.
There are also certain post-surgical risks. The pulse generator, or the wiring, can detach or prove defective. If you have a stimulator, make sure your doctors and technicians are aware before having a mammogram, ultrasound or MRI (magnetic resonance imaging). The use of a heart defibrillator can also damage the device.
Vagus Nerve and Depression
Doctors aren't exactly sure why vagus nerve stimulation (sometimes called vagal nerve stimulation) can be effective in treating depression [source: WebMD]. However, anecdotal evidence suggests that the impulses, by stimulating the brain stem, can affect the chemical balance of the mood centers of the brain and enhance the production of neurotransmitters, which have been shown to ease some depression symptoms [sources: AANS; Mayo Clinic].
Shortly after the U.S. Food and Drug Administration (FDA) approved the use of VNS for the treatment of epilepsy in 1997, researchers began to notice that the treatment showed signs of promise in treating some epileptic patients who also suffered from depression. Studies revealed little improvement after several months but a significant benefit after a year of treatments.
Based on those studies, the FDA approved VNS treatment for depression in 2005, under the very strict guidelines mentioned earlier. However, even with rigid criteria in place, the use of VNS is still somewhat controversial -- given the lack of long-term findings and uncertainty of side effects -- and is not currently covered by Medicaid.
That can be a daunting issue for patients already dealing with depression, as the initial cost of implanting a VNS device can run more than $30,000. Which doesn't include subsequent visits for monitoring and adjustments. Some private health insurers will cover some or part of this cost, but they are in the minority. Ask beforehand to avoid surprises.
Also, since vagus nerve stimulation is a relatively new depression treatment, candidates are encouraged to carefully consider the pros and cons before using it [source: Mayo Clinic]. Patients are also required to continue standard depression treatments along with VNS. According to the AANS, however, VNS should not be considered for any patient suffering from acute suicidal thoughts or behavior, schizophrenia, delusional disorders or history of rapid cycling bipolar disorder.
- AANS. "Vagus Nerve Stimulation." American Association of Neurological Surgeons. May 2007. (Feb. 2, 2012) http://aans.org/en/Patient%20Information/Conditions%20and%20Treatments/Vagus%20Nerve%20Stimulation.aspx
- Encyclopedia Britannica. "Vagus nerve." Britannica.com. 2012. (Feb. 3, 2012) http://www.britannica.com/EBchecked/topic/621522/vagus-nerve
- InnovateUs. "What is the function of the Vagus nerve?" InnovateUs.com. (Feb. 4, 2012) http://www.innovateus.net/innopedia/what-function-vagus-nerve
- Mayo Clinic. "Vagus Nerve stimulation for depression." Mayo Clinic. July 30, 2010. (Feb. 2, 2012) http://www.mayoclinic.com/health/vagus-nerve-stimulation/MY00183
- MedicineNet. "Definition of Vagus Nerve." MedTerms.com. April 27, 2011. (Feb. 2, 2012) http://www.medterms.com/script/main/art.asp?articlekey=7631
- Tian, Stan. "Vagus Nerve Disorders." HealthGuidance. (Feb. 4, 2012) http://www.healthguidance.org/entry/12041/1/Vagus-Nerve-Disorders.html
- Tracy, Natasha. "Vagus Nerve Stimulation (VNS) for Treating Depression." Healthy Place. Jan. 17, 2012. (Feb. 4, 2012) http://www.healthyplace.com/depression/depression-treatment/vagus-nerve-stimulation-vns-for-treating-depression/
- WebMD. "Epilepsy: Vagus Nerve stimulation." WebMD.com. (Feb. 3, 2012) http://www.webmd.com/epilepsy/guide/vagus-nerve-stimulation-vns
- WebMD. "Vagus New Stimulation (VNS) for Depression." WebMD.com. 2010. (Feb. 2, 2012) http://www.webmd.com/depression/vagus-nerve-stimulation