When the magnet is placed over the device, the VNS is shutdown, and stays off until the magnet is removed. This is a fail safe measure in the event the stimulator malfunctions and stays on continuously. In practice, the magnet is used as soon as the patient feels a seizure coming on. The VNS can then be activated on demand. I hope better than for epilepsy brain surgery.
Brain surgery has the ability to cure some patients and help most patients.
However, the evaluation process is expensive and difficult, partly to insure that surgery is performed ONLY on patient with real and uncontrolled seizures. This has limited the use of epilepsy brain surgery to academic centers. It will never be available in community hospitals, and thus will never be available to the 100,00 patients who might benefit. Now consider seizure medicines. There is no restriction on their use.