Pulses of electricity delivered to a precise location on the spinal cord have helped two stroke patients regain control of a disabled arm and hand, a team reports in the journal Nature Medicine.

The success should give "a lot of hope" to hundreds of thousands of people in the U.S. who've been disabled by a stroke, says Dr. Walter Koroshetz, director of the National Institute of Neurological Disorders and Stroke, which helped fund the research.

The results will need to be replicated in a larger study, Koroshetz says, adding that it's still unclear which stroke patients will benefit most from the treatment.

For Heather Rendulic, 33, one of the patients in the study, the treatment was life-changing.

As a teenager, Rendulic liked to run and ride horses. Then, beginning in 2011, she had a series of strokes caused by malformed blood vessels in her brain. The last stroke was the worst.

"I woke up and I couldn't move the whole left side of my body," Rendulic says.

Surgeons were able to remove the cluster of blood vessels that had caused her strokes. But the damage was done.

"It took me almost two years to walk on my own unassisted," says Rendulic, who wrote a book about her experiences.

Rendulic was eventually able to move her arm and hand a bit. For example, she could close her hand, but not open it. As a result, she was unable to tie her own shoes, open a jar, or chop vegetables.

"You don't realize how many things you need two hands for until you only have one good one," she says.

So nearly a decade after her strokes, Rendulic volunteered for a study at the University of Pittsburgh.

Researchers there knew that in most people like Rendulic, the brain is still trying to send signals through the spine to the muscles that control the arm and hand. Marco Capogrosso, an assistant professor in the department of neurosurgery, says the problem is that those signals are very weak.

"We wanted to pick up on these weak signals and essentially turn them into functional outputs so that a person would be able to control their own hand voluntarily," he says.

Capogrosso and a team of researchers hoped to do this by delivering pulses of electricity to nerve cells in the spine. The electricity makes these nerve cells more responsive, or excitable, which helps signals from the brain get through to the muscles they control.

When the team tried this in animals, they were able to restore arm and hand function.

"If you carefully place the electrodes inside the spinal cord, you can direct this excitability toward the muscles you need," Capogrosso says.

The team was pretty sure their approach would work in people, he says. "But we didn't expect the amount of movement recovery that we observed."

Rendulic was the first person they treated. A surgeon used a large needle to place the electrodes in her spine. "I had wires hanging out of my back," she says.

Later, in the lab, researchers turned on the stimulation. The effect was immediate.

"I was opening my hand in ways that I haven't in ten years and my husband and my mom were with us and we all were in tears," Rendulic says.

The difference is easy to see in a video made by the researchers that shows Rendulic trying to pick up a can of soup.

At first, "you can see she can't really do anything with her hand," says Elvira Pirondini, a research assistant professor in physical medicine and rehabilitation. "But when the stimulation is on she can reach the soup and she can grab the can and also elevate it."

The electrical pulses also improved something many stroke patients lose — the ability to sense the position of her arm and hand without looking at them, which comes from a sort of sixth sense known as "proprioception."

"When the stimulation was on, it was much easier for her to understand where her arm was in space." Pirondini says.

The effects of stimulation became more dramatic during the four weeks each patient had the electrodes in their spine.

"They start by opening the hand and by the end of the four weeks they can do all sorts of things," Capogrosso says.

Also, the effects diminished but did not disappear entirely when the stimulation was switched off. That suggests the pulses are causing changes to the circuits controlling the arm and hand, Capogrosso says, though it's not clear how long those changes will last.

At the end of the four-week study, the electrodes were removed from both patients. But researchers say they plan to develop a system that can be implanted permanently.

Ordinarily, moving this sort of technology from the lab to widespread use takes many years. But the process is likely to move much faster in this case because the device used to stimulate the spine is already approved by the Food and Drug Administration for treating patients with chronic pain.

"There are thousands of patients implanted with this technology," Pirondini says.

Spinal stimulation has also been used to help patients paralyzed by a spinal injury regain the ability to walk.

"I don't see any deal breakers on the way of getting this to [stroke] patients," Koroshetz says.

Rendulic says her experience has changed the way she views her future, and she hopes to be first in line to receive a permanently implanted stimulator.