Mr. Wallis’s brain scans — the first ever of a late-recovering patient — revealed changes in the strength of apparent connections within the back of the brain

Which is believed to have helped his conscious awareness, and in the midline cerebellum, an area involved in motor control, which may have accounted for the very limited movement in his arms and legs while he was minimally conscious.

Mr. Wallis, who regained some more movement after he was awakened, was diagnosed with severe quadriparesis, characterized by muscle weakness in his limbs.

“He’s a unicorn in the sense that he emerged so late,” Dr. Schiff said. But, he added, “We’ll never know exactly why he emerged after 19 years.”

Mr. Wallis’s family believes that regular visits home, while he was minimally conscious, had an impact. “We think that helped his awakening,” his brother George said.

Mr. Wallis’s recovery occurred nearly two years before the death of Terri Schiavo, a Florida woman who had suffered extensive brain damage and fell into a persistent vegetative state when her heart stopped beating in 1990. Her feeding tube had been removed after a bitter national debate over patients’ rights.

zebbi Qries