VNS offers hope for epileptics

The VNS has been tested by neurologists and may offer an alternative for controlling seizures in epileptics for whom drugs or surgery have proven inadequate.

The vagus nerve stimulator, as the device is called, has yielded promising results in early clinical tests determining its ability to control seizures.

"So far 40 percent of the patients receiving vagus nerve stimulation have had a 50 percent reduction in seizures, or better," reports Christopher DeGiorgio, associate professor of neurology and neurosurgery, who heads the Epilepsy Program here.

The stimulator, or pacemaker, consists of a tiny pair of electrodes which are implanted onto the vagus nerve in the region of the neck, and connected to a programmable generator which is implanted under the skin in the left upper chest.

The surgery to install the device takes a few hours and patients are usually able to return home in a day.

Other than thin scars on the neck and chest, and a periodic hoarsening of the voice when the stimulator turns on, patients bear no external signs of having received the implant.

Designed to stimulate the nerve at set intervals of time, the pacemaker can also be turned on externally by holding a simple magnet over the chest.

The electrodes work by stimulating the vagus nerve, a sensory and motor originating in the brain stem that enervates a number of organs including the heart, lungs, larynx, vocal cords, stomach, tongue and ears.

This stimulation in turn, appears to regulate the onset of seizures. "The cellular mechanisms underlying the effect is still under investigation," said DeGiorgio.

"An epileptic seizure is caused by an abnormal electrical discharge in the brain," he explained. "We think that stimulating the vagus nerve may abort seizures by activating inhibitory pathways in the brain. PET studies here at USC show that vagus nerve stimulation activates the thalamus and cerebellum. Inhibitory pathways may project from these areas to the surface of the brain [cortex] which is where seizures originate.

"To us the vagus nerve is like a freeway which gives us a direct route into the brain without having to open it up," he remarked.

The original idea for this approach came from experiments conducted by UCLA neuroscientist Michael Chase about 30 years ago who found that stimulating the vagus nerve in animal models changed the brain waves. The smaller faster pattern obtained correlated with an anti-convulsive effect, DeGiorgio added.