Vagus nerve stimulation is already used to help people with epilepsy and depression. This cranial nerve runs from the brain to other parts of the body, including the heart, lungs and gut; vagus means "wandering" in Latin.
The study results challenge ideas that consciousness disorders lasting longer than 12 months are irreversible, the researchers believe.
Vagus nerve activity is "important for arousal, alertness and the fight-or-flight response," wrote Dr. Angela Sirigu in an email. She is an author of the study and neuroscientist at the Institut des Sciences Cognitives Marc Jeannerod in Lyon, France.
Sirigu and her colleagues decided to test the ability of vagus nerve stimulation to restore consciousness in a patient in a vegetative state. Patients in a vegetative state show no evidence of consciousness, mental function or motor function. Unlike a coma, a vegetative state
includes intermittent periods of eye opening; this seemingly hopeful sign, though, is not a normal waking, just a random physiological occurrence.
Vagus nerve stimulation begins with a surgeon implanting a device in the chest and threading a wire under the skin. This wire joins the vagus nerve and the device, which sends electrical signals along the nerve to the brain stem (where the spinal cord and brain connect) and in turn this transmits impulses to certain areas in the brain.
Stimulating the vagus nerve activates "a natural physiological mechanism," wrote Sirigu in an email.
Sirigu and her colleagues selected the man, who had been in a vegetative state for 15 years "showing no sign of change since his car accident," she wrote. "We therefore put ourselves in a difficult challenge by selecting a patient with the worst outcome."
The reason for that choice is that if any changes occurred in the patient after vagus nerve stimulation, then "these could not be the result of chance," she added.
After a single month of stimulation, the patient's attention, movements and brain activity significantly improved, according to the authors.
"Our results show major changes at the brain level," Sirigu said. One electroencephalogram or EEG signal, "a brain rhythm previously shown to distinguish vegetative from minimally conscious state patients, significantly increased," she wrote, particularly in areas important for "movement, body sensations and awareness." A PET scan, a type of imaging test, showed increases in metabolic activity in the brain, as well.
Dr. Nicholas Schiff, a neuroscientist at Weill Cornell Medicine and NewYork-Presbyterian who also researches consciousness, said some will look at this case and say, "It's one patient, and they didn't really move him into a new functional category. And then they will say, 'What's the point here?' " said Schiff, who was not involved in this study.
Yet the new study is "another demonstration of what is possible to do, and it's a new technique, and it might have some real advantages for some patients," he said.
The human brain's 'greater potential'
"The general point here is that taken together with all the other information that we have now, it's very clear that the severely injured human brain has greater potential than it's given credit for," Schiff said. "So you can lay around for years and, in principle, still be responsive to medications, devices and other things."
Even with that much brain injury, you can still "move the dial," said Schiff.
What's new in this study is stimulation of the vagal nerve on the outside of the brain, he said. "The nerve sends impulses down into the stomach area," he explained. Instead, the researchers send impulses up through the nerve, and that activates the brain through multiple synaptic pathways.
In the United States, an estimated 50,000 patients are in a vegetative state, and about 300,000 are in a minimally conscious state, Schiff said.