Vagus nerve stimulation (VNS) is a surgical procedure that can be used to treat those with treatment-resistant depression. A pacemaker-like device, implanted in the body, is attached to a stimulating wire that is threaded along a nerve called the vagus nerve. The vagus nerve travels up the neck to the brain, where it connects to areas believed to be involved in regulating mood. Once implanted, this device delivers regular electrical impulses to the vagus nerve. How Vagus Nerve Stimulation WorksDuring surgery for VNS, your surgeon will implant a small battery-powered device -- about the size of a silver dollar -- in your chest. It works like a pacemaker. Another incision is made on the left side of the neck and a thin wire (placed just under the skin) runs from the device to the large vagus nerve in your neck. The device sends out pulses of electricity into the nerve, which transmits them to the brain. For reasons that doctors don't completely understand, these electrical impulses transmitted via the vagus nerve to the brain can relieve the symptoms of depression. The impulses may affect the way nerve cell circuits transmit signals in areas of the brain that affect mood. However, it usually takes several months before you feel the effects. Whenever it's necessary, your doctor can change the settings on the device (essentially changing the dose) in the office with a programming wand. Usually, the device is set to go off at regular intervals. You can also turn it off using a special magnet. Research into the effects of VNS on people with treatment-resistant depression has generally been positive. A study in Biological Psychiatryin 2005 compared 124 people that received usual treatment to 205 people that received usual treatment plus VNS. After one year of treatment, the combination treatment group showed more improvement than the usual treatment group. Significant improvement was seen in 27% of patients that received VNS vs. 13% that did not. VNS is not a rapid treatment for depression. Studies show that, on average, it may take up to 9 months for a treatment response to occur. VNS Risks and Side EffectsPossible side effects from VNS include temporary hoarseness, cough, and shortness of breath. Most of these side effects only occur during the 30 seconds that the stimulator is on. Like any operation, the implantation procedure poses some risks, including infection. As with pacemakers, eventually, you will need surgery to replace the battery when it wears out. In addition, though rare, damage to the device or the leads could require additional surgery prior to replacing the battery. Since the VNS device can interfere with mammograms, special positioning may be required to get the best possible image. Certain medical procedures, such as defibrillation for the heart or ultrasound, can also damage the VNS device. In addition, special precautions may need to be taken before having an MRI scan, so be sure your doctor knows.