"It was like red-hot pokers needling one side of my face," says Catherine, recalling the cluster headaches she experienced for six years. "I just wanted it to stop." But it wouldn’t – none of the drugs she tried had any effect.

Thinking she had nothing to lose, last year she enrolled in a pilot study to test a handheld device that applies a bolt of electricity to the neck, stimulating the vagus nerve – the superhighway that connects the brain to many of the body’s organs, including the heart.

The results of the trial were presented last month at the International Headache Congress in Boston, and while the trial is small, the findings are positive. Of the 21 volunteers, 18 reported a reduction in the severity and frequency of their headaches, rating them, on average, 50 per cent less painful after using the device daily and whenever they felt a headache coming on.

This isn’t the first time vagal nerve stimulation has been used as a treatment – but it is one of the first that hasn’t required surgery. Some people with epilepsy have had a small generator that sends regular electrical signals to the vagus nerve implanted into their chest. Implanted devices have also been approved to treat depression. What’s more, there is increasing evidence that such stimulation could treat many more disorders from headaches to stroke and possibly Alzheimer’s disease.

The latest study suggests it is possible to stimulate the nerve through the skin, rather than resorting to surgery. “What we’ve done is figured out a way to stimulate the vagus nerve with a very similar signal, but non-invasively through the neck,” says Bruce Simon, vice-president of research at New Jersey-based ElectroCore, makers of the handheld device. “It’s a simpler, less invasive way to stimulate the nerve.”

Cluster headaches are thought to be triggered by the overactivation of brain cells involved in pain processing. The neurotransmitter glutamate, which excites brain cells, is a prime suspect. ElectroCore turned to the vagus nerve as previous studies had shown that stimulating it in people with epilepsy releases neurotransmitters that dampen brain activity.

When the firm used a smaller version of ElectroCore’s device on rats, it found it reduced glutamate levels and excitability in these pain centres. Other studies have shown that vagus nerve stimulation causes the release of inhibitory neurotransmitters which counter the effects of glutamate.

The big question is whether a non-implantable device can really trigger changes in brain chemistry in humans, or whether people are simply experiencing a placebo effect. “The vagus nerve is buried deep in the neck, and something that’s delivering currents through the skin can only go so deep,” says Mike Kilgard of the University of Texas at Dallas. As you turn up the voltage, there’s a risk of it activating muscle fibres that trigger painful cramps, he adds.

Simon says that volunteers using the device haven’t reported any serious side effects. He adds that ElectroCore will soon publish data showing changes in brain activity in humans after using the device. Placebo-controlled trials are also about to start.

Catherine has been using it for a year without ill effect. “I can now function properly as a human being again,” she says.

The many uses of the wonder nerve

Coma, irritable bowel syndrome, asthma and obesity are just some of the disparate conditions that vagus nerve stimulation may benefit and for which human trials are under way.

It might also help people with tinnitus. Although people with tinnitus complain of ringing in their ears, the problem actually arises because too many neurons fire in the auditory part of the brain when certain frequencies are heard.

Mike Kilgard of the University of Texas at Dallas reasoned that if people were played tones that didn’t trigger tinnitus while the vagus nerve was stimulated, this might coax the rogue neurons into firing in response to these frequencies instead. “By activating this nerve we can enhance the brain’s ability to rewire itself,” he says.

He has so far tested the method in rats and in 10 people with tinnitus, using an implanted device to stimulate the nerve. Not everyone noticed an improvement, but even so Kilgard is planning a larger trial. The work was presented at a meeting of the International Union of Physiological Sciences in Birmingham, UK, last month. The technique is also being tested in people who have had a stroke.

"If these studies stand up it could be worth changing the name of the vagus nerve to the wonder nerve," says Sunny Ogbonnaya at Cork University Hospital in Ireland.