Editor’s note: The research reported on here was funded in part by the Dana Foundation. Additional news coverage and links are available here. This article is from the July 2006 Brain in the News.
In 2003, a severely brain-damaged patient named Terry Wallis first made national headlines after regaining the ability to speak, which he had lacked for 19 years. When I read those stories, I focused on what I knew had to be inaccurate in the reports rather than the possibility that such late changes could occur after very severe brain injury. Luckily, Terry Wallis eventually became more than an amazing story for our research group: he became our study patient, and he has educated us along the way.
Mr. Wallis regained his speech and the ability to make some movements after spending most of those 19 years in a minimally conscious state. After severe brain injury, patients in a minimally conscious state demonstrate intermittent but unequivocal evidence of awareness and behavioral responsiveness. Mr. Wallis’s spontaneous recovery of fluent speech has continued, with further gradual clinical improvements including improved motor functions.
Other reports of such late recovery of communication and goal-directed behavior following stable behavioral levels consistent with the minimally conscious state have appeared in the popular press, yet none of these patients have previously been evaluated with brain imaging and reported in the scientific literature. In a research article published in the July issue of the Journal of Clinical Investigation, Henning Voss, a physicist at the Weill Cornell Citigroup Biomedical Imaging Center, and I, along with our colleagues, report on detailed anatomical and metabolic measurements of Mr. Wallis’s brain.
What allowed for this recovery after such a lengthy period remains a mystery but may in part be explained by what is called axonal regrowth, where brain cells form new connections. Our group tracked changes in Mr. Wallis’s brain structure and function in studies that began about nine months after recovery. We used diffusion tensor imaging (DTI), a type of detailed structural imaging, as well as positron emission tomography (PET), a technique that precisely measures brain metabolic activity.
DTI allows scientists to look at the direction of water molecules as they move around brain cells. From these measurements it is possible to infer the integrity and direction of white matter tracks in the brain. DTI is a technology available only at research institutions and is not yet used in hospital settings.
Mr. Wallis’s structural brain imaging studies revealed extensive cerebral and subcortical atrophy, or tissue loss, particularly affecting the brainstem and frontal lobes. Throughout the brain, there was marked reduction of volume and ventricular enlargement. Precise measurements of white-matter regions using diffusion tensor imaging data revealed evidence of very severe, widespread axonal injury, a common mechanism of brain damage following traffic accidents.
The volume of the medial corpus callosum, a white-matter structure that connects the two hemispheres of the brain, was one-third to two-thirds smaller than normal, a sign of the severity of the overall brain injury.
Surprisingly, in addition to the severe reduction of brain connectivity demonstrated in the DTI data, Mr. Wallis also showed unusual large regions of increased strength of connectivity and a preferred common apparent direction of these connections in posterior brain structures not seen in 20 normal subjects.
These large, bilateral regions of white matter changed to become consistent with normal values when measured in a second DTI study 18 months later. In contrast, we saw changes within the middle regions of the cerebellum, a brain structure involved in movement control. These changes in cerebellar white matter in the second study correlated with evident clinical improvements in Mr. Wallis’s motor functions. Both findings were further correlated with increased resting metabolism, measured by PET in the subregions demonstrating these inferred changes in white matter fibers.
Most notably, Mr. Wallis’s recovery of movement of both lower extremities, including the ability to bridge his lower back to assist in transfer—a critical help to his caregivers—was very unexpected. In fact, when Mr. Wallis’s family asked us during his first evaluation whether there was any likelihood that he might recover motor function, we expressed the firm opinion that it would not be possible.
Collectively, the findings raise the possibility that reconnection among existing neurons may play a role as a slow variable of structural change during recovery from severe brain injury. It is most likely that instead of a "sudden recovery" after 19 years, the recovery took place slowly, possibly as new nerve connections gradually were made. We suspect that other factors also played a role in promoting his recovery; however, because no earlier imaging studies or other evaluations are available, we will never really know in Mr. Wallis’s case what sequence of events led to his remarkable story. The findings underscore the need to develop studies to better understand the mechanisms underlying recovery of consciousness and communication following severe brain injuries.