Having used vagus nerve stimulation, researchers restored consciousness to a man who had been in a vegetative state for 15 years.
Published in the journal Current Biology, the finding appears to challenge the view that it is impossible to restore consciousness in cases where there has been more than 1 year of "unresponsive behavior."
Co-lead investigator Dr. Angela Sirigu, of the Institut des Sciences Cognitives Marc Jeannerod in Lyon, France, comments that their results show that "it is possible to improve a patient's presence in the world" by stimulating the vagus nerve.
The vagus nerve links the brain to the larynx, pharynx, heart, lungs, gut, and other parts of the body. It plays an important role in alertness and waking, and in essential functions not directed consciously (such as digestion, breathing, and heartbeat).
Classed as a "mixed nerve," the vagus nerve consists partly of fibers that carry signals out from the brain, and partly of fibers that convey signals into the brain from the body.
Improvements in behavior
Dr. Sirigu and colleagues wanted to find out whether or not vagus nerve stimulation could restore consciousness. They chose a patient who had been in a vegetative state for more than 10 years with no signs of improvement in order to reduce the likelihood that any improvements might occur by chance.
"Following the hypothesis that vagus nerve stimulation functionally reorganizes the thalamo-cortical network," they explain in their report, "we tested its effects on the cortical activity of a patient lying in a vegetative state for 15 years following traumatic brain injury."
The team implanted a vagus nerve stimulator into the 35-year-old male patient's chest and gradually increased the stimulation current to a maximum of 1.5 milliamps.
After 1 month of vagus nerve stimulation, the patient began showing signs of improvement, both in measures of behavior and brain activity.
For example, his attention and movements improved: his eyes could follow a moving object, and he moved his head when asked to. His mother also reported that he was better able to stay awake and listen when his therapist read him a book.
There were also other responses that had not been present before the stimulation, such as reacting with wide-eyed surprise when someone approached his face suddenly.
As well as noting improvements observed by clinicians and family members, the team also found improvements in scores of a test called the Recovery Scale-Revised (CRS-R) test.
The CRS-R test improvements were mostly in the "visual domain," and as stimulation increased, the scores rose from 5 (the last measure before implantation) to 10 at the highest level of stimulation.
Scans confirm improved brain activity
There were also some major changes in brain activity, as seen in before and after results of electroencephalography (EEG) and 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET).
For instance, a brain signal "found to reliably distinguish minimally conscious patients from vegetative ones" - called the "theta EEG signal" - improved significantly in parts of the brain that deal with sensation, awareness, and movement. The PET scans confirmed many of the findings of the EEG recordings.
On the findings, the authors note that they "show that stimulation of the vagus nerve promoted the spread of cortical signals and caused an increase of metabolic activity" that, in turn, led to the measured and observed improvements in behavior.
They conclude that their findings suggest that the right intervention can bring about changes even in the most severe cases of vegetative state.
"Brain plasticity and brain repair are still possible even when hope seems to have vanished."
Dr. Angela Sirigu
The team is now planning to take the findings to the next level with a large study involving several patients. Dr. Sirigu says that their findings also shed new light on the mind's "fascinating capacity" to "produce conscious experience."