Courtesy of the Wallis family/Getty Images
Terry Wallis (left) in 1984 just prior to his catastrophic car accident and in 2003 (right) after awakening from a minimally conscious state after 19 years.
When Angilee Wallis entered her son Terry’s nursing home room on June 12, 2003, he looked at her and said "Mom." It was the first word he had uttered in 19 years.
Now, 3 years after Terry Wallis’s return to the land of the living, a team of researchers at Weill Medical College of Cornell University has completed a landmark study of his brain. Using advanced imaging technology they captured the new neural connections snaking through his damaged brain, and in the process overturned medical dogma on the brain’s capacity to heal itself.
Into Darkness
A catastrophic car accident in 1984 left Wallis with massive brain injuries. After 1-2 weeks in a coma, he awakened partially and his condition was reclassified as a persistent vegetative state (PVS), a medical diagnosis that received enormous media attention last year during the legal battle over Terri Schiavo.
Courtesy of Henning Voss at Weill Medical College of Cornell University Conventional MRI of Terry Wallis (top) and a healthy individual (bottom) shows that Wallis has less total white matter than a healthy person, but does not reveal the new axon growth that made his recovery possible.
Courtesy of Henning Voss at Weill Medical College of Cornell University
In the months following the accident, Wallis progressed from the vegetative state to a condition that later came to be known as the minimally conscious state (MCS). There is no clear record of Wallis’s shift, because MCS did not formally enter the medical lexicon as a distinct syndrome until 2002, when neurologists refined the classifications of severely brain-damaged patients to take into account the fact that some showed sporadic signs of responsiveness. Typical of patients in MCS, Wallis would sometimes grunt or blink in response to commands or inquiries; his family insisted throughout the ordeal that his face registered their arrival and that his expression changed when he was hungry or impatient. (This minimal level of responsiveness distinguishes Wallis’s condition from that of Terri Schiavo.) But none of his responses amounted to genuine communication, and after 19 years, doctors held out no hope of meaningful recovery.
Following the Water Trail
Susumu Mori/John Hopkins University
A comparison of a brain scan using diffusion tensor imaging (left) and magnetic resonance imaging (right).
Yet Terry Wallis regained consciousness, and his awakening has shaken and reinvigorated the field of neurology. While it was obvious from his behavior that Wallis’s condition had improved, a relatively new technique called diffusion tensor imaging (DTI) allowed researchers to get a clear picture of the physiological changes that underpinned his recovery.
A type of magnetic resonance imaging (MRI), DTI works by tracking the diffusion of water molecules through brain tissue. In a uniform medium, like a glass of water, diffusion is isotropic, meaning that it occurs equally in all directions. But because brain tissue is far from uniform, water diffusion through the brain is anisotropic—it has a direction. Specifically, a water molecule inside an axon (a long, snaky nerve cell that transmits electrical signals through the brain and body) is far likelier to travel within the axon than to cross the myelin sheath into the surrounding tissue. Water therefore diffuses in channels, following the direction of the axon. By tracking the movement of water molecules, diffusion MRI in essence creates a map of the brain’s white matter. (Brain tissue is divided into white matter, which consists primarily of myelinated axons and is responsible for transmitting information, and gray matter, which is responsible for processing information.) Introduced in the mid-1990s, DTI is an improvement on older diffusion MRI technology in that it is specifically designed for 3-D imaging; the T stands for tensor, a mathematical concept that generalizes the idea of a vector, or directed quantity, to convey additional information beyond magnitude and direction.
Axed Axons Re-expand
Lead researcher Henning Voss and colleagues at Cornell performed DTI scans on Wallis in April 2004, eight months after he uttered his first words. For comparison, they also scanned a patient who had been in MCS for six years and showed no signs of recovery, as well as 20 healthy controls. Both Wallis and the second patient had less white matter overall than the healthy individuals—no surprise, since each had suffered serious brain damage. Wallis’ scan, however, showed axon bundles in certain regions of the brain that were actually thicker than those of healthy people. One of the most active areas was the precuneus, which neurologists believe is important for wakeful consciousness. In healthy subjects, the precuneus displays minimal activity during sleep or anesthesia.
Courtesy of Henning Voss at Weill Medical College of Cornell University
Diffusion tensor imaging illuminates new, highly active axon regions in Wallis’s brain. Colors indicate axons’ direction: red for fibers going from right to left, blue for those that run front to back. Arrows on each scan, which were taken 18 months apart, point to new growth regions. Neurologists were intrigued to find that between the two scans, some new fibers faded while others strengthened, as Wallis’s damaged brain continued to re-forge lost connections.
In addition to being unusually dense, Wallis’s axons displayed a strikingly different pattern than those of a normal brain. Where typically neurons would stretch directly across from one side of the brain to the other, in Wallis, connections snaked along the back of the brain, bypassing severely damaged areas.
Voss’s team concluded that Wallis had grown new axons before, during and after his recovery, as the damaged parts of his brain attempted to restore connections severed in the accident. Since they did not have scans of his brain from before the recovery, there was no way to tell exactly when or how quickly the new connections were forged. The scans left no doubt, however, that the areas with the highest level of axon growth were precisely the regions in which Wallis had recovered the most function. Patient #2, meanwhile, showed no signs of new axon development.
A second set of scans, taken 18 months after the first set, cemented the notion that Wallis’s brain was growing new connections. While the regions that had been hyperactive in the first scan calmed to normal levels, regions involved in motor control now showed unusually high axon concentration. In fact, in the time between the two scans, Wallis, who remains largely paralyzed, did recover some movement, including the ability to stretch his legs and somewhat control his left arm. Since scan #2 showed axons not present in scan #1, there was no doubt that Wallis was growing new brain connections.
Wake-Up Call: Miraculous Recovery Shows Brain Can Heal
Linear Mode
