They believe intensive physiotherapy is the key to the modest, but important, changes Reeve has seen since his injury in 1995.
However, they cannot predict whether improvement will continue or if the same approach will help others with long-term paralysis.
“We are talking about an unprecedented amount of recovery. There is just no basis to talk about how much more to expect,” said neuroscientist Naomi Kleitman, head of spinal cord injury research at the National Institute of Neurological Disorders and Stroke.
The first clear sign of change occurred one early November day almost two years ago, when Reeve twitched his left index finger.
By then, he had been immobile from the neck down for more than five years, unable to feel or move anything. But the movement was the start of a slow rebirth of sensation and control that he says has changed his life for the better.
Reeve, who is 50 on September 25, must still use a wheelchair. All but one hour a day, he uses a ventilator to breathe. But he can feel human touch, experience pain and move his fingers, wrists and legs.
“His was the worst-case scenario,” said Dr John McDonald, who oversaw his treatment at Washington University School of Medicine in St Louis. “Nobody in the world would have predicted he could recover.”
Reeve was thrown from a horse seven years ago and landed on his helmet, breaking his neck and damaging the thumb-size bundle of nerves that carries messages between the brain and the rest of the body.
At least three-quarters of the nerve fibres were severed, and what remained did not work.
Over the years, his muscles withered, his bones thinned, and he suffered repeated bouts of infection and life-threatening complications.
After years of his own exercise efforts, the actor began in April 1999 an approach called activity-based recovery, which involves repeated electrical stimulation of the muscles. The idea is that constant motion could re-educate the remaining nerves in the spine to carry signals and perhaps even sprout new branches to connect to healthy fibres above and below the injury.
Now, Reeve can tell hot from cold. He can feel about two-thirds of the normal sensation of being touched and half of the usual intensity of pinpricks.