Injury to the brain may tear the nerve fibers that relay messages between different regions, impeding the integration process. Similarly, Schiff believes that the circuits left intact in minimally conscious and vegetative patients may communicate erratically, making it difficult for the brain to coördinate complex tasks involving multiple brain areas. Patients with impaired consciousness also exhibit low levels of neural activity, Schiff says; their brains may take a stab at a particular task, generating the brief appearance of responsiveness, but then peter out. A patient’s occasional moments of clarity, then, might come from brief spurts of synchronized activity. “Some patients may harbor the capacity for functional recovery, but it depends on recruiting circuit-level neuronal responses to sustain a state like that of the brain working normally,” Schiff says. Emotional events, such as a sister’s description of childhood memories, may do a better job of activating those circuits, which could explain why emotional stories seem to trigger the strongest responses.
Understanding what causes impairments in consciousness could ultimately shed light on a larger puzzle: what allows a healthy person to be aware of self and surroundings? “I think that a detailed understanding of the necessary and sufficient conditions for the recovery of consciousness will provide immensely important insights into the fundamental nature of the human conscious state,” says Schiff.
Schiff’s ultimate goal, of course, is to spark awakenings like that of Terry Wallis in other minimally conscious patients. At a neuroscience meeting last October, he presented preliminary evidence that electrically stimulating the thalamus, which sends sensory information to the cerebral cortex, might help patients recover consciousness. Schiff and his team used deep brain stimulation–a therapy used to treat Parkinson’s disease, where an electrode is implanted in the brain–to stimulate thalamic neurons in a 38-year-old minimally conscious patient who had suffered a severe traumatic brain injury six years before. They found that when the neurons were stimulated, the patient was more responsive and coördinated, even able to eat a meal with some independence.
Though Schiff is reluctant to talk about his group’s findings before they are published in a peer-reviewed paper, he and other neurologists are clearly excited about them. “This is a very interesting and important observation,” says James Bernat, a neurologist at Dartmouth Medical School, who adds that Schiff’s result is particularly noteworthy because the patient had been in a minimally conscious state for so long. Previous studies of deep brain stimulation, carried out mostly in Japan, have involved recently injured patients, who might have improved anyway.
To prove the efficacy of deep brain stimulation in treating consciousness disorders, and to determine just which patients it might help, other researchers will need to duplicate Schiff’s success. But that’s a tall order. Research on minimally conscious and vegetative patients presents enormous obstacles–the logistics of transporting patients from long-term-care facilities to imaging labs, the ethical and legal issues involved in testing people who cannot give informed consent, and the technical challenge of scanning patients who may move unpredictably and may not be able to comprehend instructions to stay still.
But the biggest barrier to larger studies is funding. Terry Wallis is one of the most remarkable recovery cases Schiff has ever seen. And yet he’s examined him just twice: first when a British television station flew Wallis and his family from Arkansas to New York, where Schiff and collaborators could scan his brain; and then when the producers of an HBO documentary paid Wallis’s fare to New York 18 months later, so that scientists could assess the changes that had taken place since the first scan.