The Vagal nerve stimulator was first introduced in the year 1988 and was approved for use in epilepsy by the US FDA in 1997. The vagus nerve or the tenth cranial nerve, unlike the other cranial nerves, has a vague (hence the name) course in the brain and has a widespread influence on different areas of the brain. It also controls the muscles involved with swallowing, speaking and coughing.
	The VNS is a pulse generator similar to the heart pacemaker, which is inserted into a small cavity in the chest wall below the left collarbone. The pacemaker is then connected via an under-the-skin cable to an electrode fitted around the left vagus nerve. The pulse generator is then programmed to generate electrical signals 24 hours a day, typically for 30 seconds every 5 minutes; the size of the current varying between one and three mA. The device is usually activated two weeks after the surgery. The level of stimulation is subsequently adjusted to suit the requirements of the individual patient. In some individuals, a burst of energy can be generated during the preictal period by passing a magnet over the device.
	The VNS may take upto one year to become fully effective. If, however, no improvement is observed upto eighteen months, the individual may choose to have his generator switched off or removed.
	Mechanism of action of the VN Stimulator       The precise mechanism of action of VNS is unknown. Unlike the various antiepileptic medications, it has been hypothesized that VNS is likely to have more diffuse effects on the various neural circuits in the brain.
	Suitable candidates:
	VNS is suitable for people with complex partial seizures and generalized seizures, where consciousness is lost. Individuals with epilepsy as a result of head injury and individuals with photosensitive epilepsy can also benefit from VNS. VNS is generally used in patients with intractable epilepsy, who have failed to respond adequately to other available treatments; i.e., multiple antiepileptic drugs.     Advantages:     Studies have reported an approximately 25-30% reduction in seizure frequency; however patients do not become seizure-free.     VNS allows for reduction in antiepileptic medications, thus decreasing the side-effects of the anticonvulsant medications.     VNS shortens the duration of seizures and the recovery time after a seizure occurs.     In some individuals, VNS may enhance mood, memory and alertness and may also help lift depression; thus improving their quality of life.   Side-effects:       Overall, VNS has been shown to be relatively safe with few side effects. The general risks associated with surgical procedures such as infection, bleeding and problems with anesthesia exist with implantation of the stimulator but these are rare. Hoarseness, difficulty in swallowing and throat pain felt when the stimulation is on are the most commonly reported side effects and affect up to a third of patients. Of theoretical concern are cardiac side- effects, but there is as yet no evidence of the same. A single case of development of psychosis following control of seizures with VNS has been reported.     Care and Precautions:   The device is powered by an internal battery that usually lasts upto 10 years. When the battery is low, it can be replaced by a small surgical procedure.     Individuals with the stimulator must try to avoid microwaves and radios.   The magnetic field of the MRI scans can cause the VNS to heat up and must be prescribed with care.