Vagus Nerve Stimulation for Depression

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?

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.

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.