When we lose a limb, the brain never stops missing it. So much so that it reaches out to make a new connection — and keeps trying years after that limb is gone.

According to a new study, that may be how amputees could someday control robotic arms, long after they’ve lost their real limbs.

The study, published in the science journal Nature, looked at a specific area in the brain of rhesus monkeys. The monkeys were each missing an arm due to accidents they had suffered at an early age, one of them from as long as 10 years earlier.

When looking at the part of their brain that control the arms, researchers found a high-degree of neural plasticity, a term used to describe neurons changing form and function to suit the environment. In other words, cells in that area of the brain were adapting and looking to forge fresh connections with limbs.

They never quit on their missing limbs.

So the researchers literally lent the monkeys a hand — a robotic grip the monkeys used to reach toward a target object, grasp it and pull it back. And they managed it with little more than impulses from their mind and a brain-machine interface (BMI).

It's all about learning

"That’s the novel aspect to this study, seeing that chronic, long-term amputees can learn to control a robotic limb," Nicho Hatsopoulos, a professor at the University of Chicago, and senior author of the study, told Neuroscience News. "But what was also interesting was the brain’s plasticity over long-term exposure, and seeing what happened to the connectivity of the network as they learned to control the device."

Indeed that plasticity — the brain cells that kept trying to built new connections to the arms — didn’t seem affected by the years that had passed.

"Connections were shedding off as the animal was trying to learn a new task, because there is already a network controlling some other behavior," Karthikeyan Balasubramanian, the researcher who led the study, told Neuroscience News. "But after a few days it started rebuilding into a new network that can control both the intact limb and the neuroprosthetic."

We’ve seen cases of people who are paralyzed being able to control robotic hands with help from a special interface in their brain in the past. But this study represents the first time amputees have been able to do so.

And that could spell a major breakthrough for limbs that don’t seem quite so robotic, but as smooth, swift and natural as thought itself.