A new version of Guttag's VNS device, which will be tested on between 10 and 20 patients over the next few months, attempts to solve this problem by providing the device with feedback from the patient. The patient's brain activity will be monitored using an electroencephalogram (EEG) that is continuously analyzed by a detection program. When a seizure is detected, the device will activate an electromagnet hung over the patient's chest, which, in turn, will activate the implanted VNS device.

Initially, the EEG electrodes will be worn as part of a device that looks like a swimming cap, says Guttag. It wouldn't have to be worn all the time, but could be used, for example, when driving. And the long-term goal is a much less conspicuous object ("We could easily put it under a hair piece"). Eventually, the electrodes could be placed permanently under the scalp, he says. Similarly, the electromagnetic triggering mechanism would be integrated within the implanted VNS device. The mechanics of this proof-of-principle set-up are still crude, says Schachter, but the all-important algorithms are reliable.

In fact, the goal is a detection program good enough to sense a seizure much earlier than a patient could. If so, such a device would not only dramatically reduce the severity of seizures, but also might also prevent them.

Another device for detecting seizures, the Response Neurostimulator, developed by NeuroPace in Mountain View, CA, is also under development and currently undergoing clinical trials. And it also involves trying to detect seizures at an early stage. However, instead of stimulating the vagus nerve, it electrically stimulates the brain directly via electrodes implanted on the surface of or inside the brain.

In theory, NeuroPace's device should have an easier job of detecting the seizure, says Brian Litt, a neurologist and bioengineer at the Hospital of the University of Pennsylvania, in Philadelphia, because such detection electrodes can be placed directly on the brain. In contrast, scalp electrodes tend to pick up much noisier signals, he says.

As far as Guttag is concerned, though, VNS has a clear advantage: "It's less invasive, because we're not actually putting anything in the brain." Indeed, a VNS device that could operate automatically would be welcomed by patients, says Litt. If successful, it could do for epilepsy what pacemakers and implantable defibrillators have done for heart conditions, he says. "At the moment, it's the equivalent of saying ‘when you feel a potentially fatal heart rhythm coming along hit yourself in the chest'."