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A new technology could some day help paralyzed patients move their limbs.

A brain-machine technology delivers messages from the brain directly to the muscles — bypassing the spinal cord — to enable voluntary and complex movement of a paralyzed hand. 

"We are eavesdropping on the natural electrical signals from the brain that tell the arm and hand how to move, and sending those signals directly to the muscles," said Lee E. Miller, lead author of the study.

The research, published in Nature, was done in monkeys, whose electrical brain and muscle signals were recorded by implanted electrodes when they grasped a ball, lifted it and released it into a small tube. 

Those recordings allowed the researchers to develop an algorithm or "decoder" that enabled them to process the brain signals and predict the patterns of muscle activity when the monkeys wanted to move the ball.  

The researchers from the Northwestern University Feinberg School of Medicine gave the monkeys a local anesthetic to block nerve activity at the elbow, causing temporary, painless paralysis of the hand. 

With the help of the special devices in the brain and the arm — together called a neuroprosthesis — the monkeys' brain signals were used to control tiny electric currents delivered in less than 40 milliseconds to their muscles, causing them to contract, and allowing the monkeys to pick up the ball and complete the task nearly as well as they did before.  

In the new system Miller and his team have designed, a tiny implant called a multi-electrode array detects the activity of about 100 neurons in the brain and serves as the interface between the brain and a computer that deciphers the signals that generate hand movements.

"We can extract a remarkable amount of information from only 100 neurons, even though there are literally a million neurons involved in making that movement," Miller said. 

"One reason is that these are output neurons that normally send signals to the muscles. Behind these neurons are many others that are making the calculations the brain needs in order to control movement. We are looking at the end result from all those calculations," he added.