In 2003, 19 years after a car accident left him in a minimally conscious state, 39-year-old Terry Wallis spontaneously started to speak. Now, using specialized MRI scans, researchers have examined Wallis's brain and found remarkable changes in his white matter. The findings could one day help scientists understand what happens in the brains of minimally conscious patients and how new interventions might rouse them back to full awareness.

Diffusion tensor images of a brain at the first scan (left) and 18 months later (right). Color shows direction of white matter fibers, e.g., green for anterior-posterior fiber tracts. Large red area in second scan (arrow) shows what scientists think is growth of new neural processes in a part of the brain that controls movement. (Credit: Weill Cornell Citigroup Biomedical Imaging Center/Henning U. Voss.)

Minimal consciousness is not uncommon after a severe brain injury, affecting at least 25,000 people in the United States. But unlike a coma, which usually lasts only a few weeks after an accident, a minimally conscious state can be prolonged for months or years. Patients are for the most part unaware of their surroundings and unable to communicate, but they may occasionally utter words, reach for objects, or respond to questions. (This condition is distinct from the vegetative state, which can also last for months or years but is not characterized by such intermittent awareness.)

Scientists know very little about what happens in the brain during such long stretches of impaired consciousness. Both human and animal research in recent years has shown that the adult brain has some capacity for self-repair. Stroke patients, for example, can sometimes recover speech or motor function as neural pathways in the brain reorganize to compensate for injured areas. And some patients do regain consciousness after months or even years, as in Wallis's remarkable case. But doctors don't yet know how to predict who will get better, and few treatments exist to boost whatever innate reorganization takes place. New brain imaging techniques, such as those used to generate the scans of Wallis's brain, could help change that.

Wallis's recovery began with one word, "mom." Though such utterances are not unknown in minimally conscious patients, his doctors and family were surprised when his speech continued to improve. To try to find out the source of Wallis's rare return to consciousness, a team led by neurologist Nicholas Schiff, of the Weill Medical College of Cornell University in New York, used a new variation of magnetic resonance imaging called diffusion tensor imaging (DTI). This technique can give scientists a detailed picture of the brain's fiber tracts -- the neural processes that relay messages between different parts of the brain. (See TR10: Diffusion Tensor Imaging, March/April 2006.) It had never been used to examine a minimally conscious patient before.

The first DTI scan, recorded eight months after his first words, showed that Wallis had profound brain damage. Compared with the brains of 20 normal subjects, both the overall structure and the neural fibers of his brain showed severe degeneration. "That in itself is a major piece of knowledge -- that he could have this much injury and still have this kind of recovery years later," says Schiff.

But scientists also discovered that a large area in the back of his brain appeared to have more fibers than normal, all oriented in the same direction -- hinting that new pathways had sprouted to connect different brain structures. This unusual pattern encompassed a part of the brain known as the precuneus, which is highly active during conscious wakefulness but less active during sleep or anesthesia, says Steven Laureys, a neurologist at the University of Liege in Belgium.