Severed victims can walk again.

• Position: Spinal Cord

When someone's spinal cord is completely severed, brain signals no longer can reach the legs to tell that person to walk. However, a University of Michigan, Ann Arbor, study demonstrates that the muscle activity necessary to walk can be generated independent of brain signals. While many studies have shown that locomotor training, such as working with patients on treadmills, is a viable therapy, assistant professor of kinesiology Dan Ferris has demonstrated that adding weight to the limbs during therapy can provide an important sensory cue to help regain walking.

He also found that moving one leg in therapy can help activate muscles in the opposite leg. "Nobody has been able to show that in humans before. It appears there are left-to-right connections in the signal in the spinal cord, not just connections from the brain to the legs."

Ferris worked with four patients with clinically complete spinal cord trauma, doing approximately 30 sessions with each over about 1 1/2 years. They hooked each subject into a harness suspended over a treadmill. Trainers helped move the subjects' legs as they stepped on the treadmill. When the patients were positioned so that just one leg...