Wallis showed few outward signs of consciousness, but his brain was methodically rebuilding the white-matter infrastructure necessary for him to interact with the outside world, researchers reported yesterday in the Journal of Clinical Investigation.
``I believe it's a very, very slow self-healing process of the brain," said Henning Voss, lead author of the study and a physicist at Weill Cornell Medical College's Citigroup Biomedical Imaging Center.
Wallis emerged from a minimally conscious state in 2003 at the age of 39 and uttered his first word since Ronald W. Reagan was in the White House: ``Mom." Since then, the onetime mechanic from Big Flat, Ark., has regained the ability to form sentences and recovered some use of his limbs, though he still can't walk or feed himself.
Using both PETscans (Positron Emission Tomography scans) and an advanced imaging technique called diffusion tensor imaging, the researchers examined Wallis's brain after he regained full consciousness, and found that cells in the relatively undamaged areas had formed new axons, the long nerve fibers that transmit messages between neurons.
``In essence, Terry's brain may have been seeking out new pathways to reestablish functional connections to areas involved in speech and motor control -- to compensate for those lost due to damage," said the study's senior author, Dr. Nicholas Schiff, a neurologist at the Weill Cornell Medical College in New York.