The case, published in the journal Current Biology, shows that vagus nerve stimulation (VNS) - a treatment already in use for epilepsy and depression - can help to restore consciousness even after many years in a vegetative state.
The outcome challenges the general belief that disorders of consciousness that persist for longer than 12 months are irreversible, the researchers said.
"By stimulating the vagus nerve, we show that it is possible to improve a patient's presence in the world," said Angela Sirigu, from the Institut des Sciences Cognitives Marc Jeannerod in France.
The vagus nerve connects the brain to many other parts of the body, including the gut. It is known to be important in waking, alertness, and many other essential functions.
To test the ability of VNS to restore consciousness, the researchers wanted to select a difficult case to ensure that any improvements could not be explained by chance.
They looked to a patient who had been lying in a vegetative state for more than a decade with no sign of improvement.
After one month of vagal nerve stimulation, the patient's attention, movements and brain activity significantly improved. The man began responding to simple orders that had been impossible before.
For example, he could follow an object with his eyes and turn his head upon request. He also showed an improved ability to stay awake when listening to his therapist reading a book.
Recordings of brain activity also showed major changes.
The theta EEG signal - important for distinguishing between a vegetative and minimally conscious state - increased significantly in areas of the brain involved in movement, sensation, and awareness.
VNS also increased the brain's functional connectivity. A PET scan showed increases in metabolic activity in both cortical and subcortical regions of the brain, too.
The findings show that the right intervention can yield changes in consciousness even in the most severe clinical cases.
"Brain plasticity and brain repair are still possible even when hope seems to have vanished," Ms Sirigu said. The researchers are now planning a large collaborative study to confirm and extend the therapeutic potential of VNS for patients in a vegetative or minimally conscious state.
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