Patients who lose consciousness for more than a year are considered extremely unlikely to regain it, but a 35-year-old Frenchman who had been in a vegetative state for 15 years has shown hints of awareness after having key brain regions electrically stimulated, scientists reported on Monday.
The patient was able to follow an object with his eyes, turn his head when asked to, and widened his eyes in surprise when a researcher’s head came close to his face — none of which he did in a vegetative state. Although he is far from recovered, and although hopeful results in one patient don’t mean the technique will work for others, the study adds to evidence that there might be a way to restore consciousness to some patients — even years later.
The new report shows that even in a very low functioning brain, “a shift in observable behaviors from none — a vegetative state — to some limited ones — a minimally conscious state — can occur,” said Dr. Nicholas Schiff, a neurologist at Weill Cornell Medicine and New York Presbyterian, who was not involved in the current case. He led a 2007 study in which a minimally conscious patient (a person who shows occasional intention, attention, awareness, and responsiveness) improved somewhat with deep brain stimulation of the thalamus.
Unfortunately, while the French patient, Schiff’s, and a few others have been “awakened” by some sort of brain stimulation, those individual successes have yet to translate into help for thousands of vegetative or minimally conscious patients. There is “strongly accumulating evidence that it is possible in many cases to increase brain activity [long] after severe injury,” Schiff said, but “there is essentially no infrastructure to have clinical follow-up” or even “larger investigative studies.”
The new case involved a Frenchman whose brain damage, suffered in a car accident, left him completely unresponsive and unconscious, known as a vegetative state. He became minimally conscious, responding to some signals from the outside world, after a month of having his vagus nerve — which runs from the abdomen to the brain, where it has numerous connections to regions that the researchers call “a hot zone for conscious awareness” — stimulated with a device implanted in his chest.
Brain imaging and electrical recordings of brain activity (EEG) showed changes that likely account for his improvement, scientists led by Angela Sirigu of France’s National Center for Scientific Research reported in Current Biology.
UCLA psychologist Martin Monti, an expert on consciousness who has used ultrasound directed at the thalamus to awaken a coma patient, said the French study seemed solid. And brain recordings offered additional evidence that something significant had changed.
The man had stronger brainwaves called a theta signal, which is absent in the vegetative state but present with minimal consciousness. In particular, theta activity increased at the junction of three brain areas: the parietal region, just behind the crown of the head, which perceives sensory information and integrates it into the mysterious state called consciousness; the temporal lobe, behind the temples and responsible for making sense of sound; and the occipital lobe, located at the bottom back of the brain and responsible for processing vision. This junction is the consciousness “hot zone.”
Different brain regions also seemed more strongly connected. Although the physical basis of consciousness is one of the deepest enigmas in biology, the best guess is that it arises from coordinated activity between the cortex and the thalamus, a switching station for sensory and motor signals, and within the cortex, which handles higher-order cognitive functions. When connectivity between and among these regions increase for whatever reason, people in minimally conscious states spontaneously recover. In this case, the “whatever reason” was vagus nerve stimulation.
Though that seems like the vagus is punching above its weight, in fact this nerve keeps wowing neuroscientists with its powers. In this case, its apparent consciousness-raising effects stem from the multiple and far-flung connections it makes throughout the brain directly or indirectly, including with the thalamus. As best Sirigu and her colleagues can tell, stimulating the vagus seems to knit together a consciousness network that had been shredded by the man’s brain injury.
By stimulating the vagus nerve, it is therefore “possible to improve patients’ presence in the world,” she said, challenging the belief that disorders of consciousness lasting longer than a year are irreversible.
She is confident the man did not go from a vegetative state to minimal consciousness spontaneously. His partial recovery coincided with the vagus stimulation, and after 15 years it seemed unlikely his improvement was due to anything else. It “could not be the result of chance,” Sirigu said.
The French case brings to at least four the number of patients “awakened” by a brain-based intervention, including Monti’s at UCLA. But he was in a coma for only a couple of weeks. Schiff and his colleagues used an electrode implanted in the thalamus to restore some brain activity to a patient who had been in a minimally conscious state for 21 years, they reported last year, though the change did not bring about real-world improvements.
Sirigu’s approach was “the same as what I and [Schiff] did,” Monti said, except it stimulated the thalamus indirectly, via the vagus, rather than directly.
If the thalamus really is the door to consciousness, why don’t physicians try stimulating it to bring back thousands of vegetative and minimally conscious patients? “Maybe it just needs time?” Monti wondered.