Researchers at Northwestern University have developed a neuroprosthesis that restores complex movement in the paralyzed hands of monkeys. By implanting a multi-electrode array directly into the brain of the monkeys, they were able to detect the signals that generate arm and hand movements. These signals were deciphered by a computer and relayed to a functional electrical stimulation (FES) device, bypassing the spinal cord to deliver an electrical current to the paralyzed muscles. With a lag time of just 40 milliseconds, the system enabled voluntary and complex movement of a paralyzed hand.
The experiments were carried out on two healthy monkeys, whose electrical brain and muscle signals were recorded by the implanted electrodes when they grasped, lifted and released a ball into a small tube. Using these recordings, the researchers developed an algorithm to decode the monkeys’ brain signals and predict the patterns of muscle activity that occurred when they wanted to move the ball.
The monkeys were then given an anesthetic to locally block nerve activity at the elbow, resulting in temporary paralysis of the hand. The multi-electrode array and FES device – which combine to form the neuroprosthesis – allowed the monkeys to regain movement in the paralyzed hand and pick up and move the ball with almost the same level of dexterity as they did before the paralysis.
“The monkey won’t use his hand perfectly, but there is a process of motor learning that we think is very similar to the process you go through when you learn to use a new computer mouse or a different tennis racquet. Things are different and you learn to adjust to them,” said Lee E. Miller, the Edgar C. Stuntz Distinguished Professor in Neuroscience at Northwestern University Feinberg School of Medicine and the lead investigator of the study.
Dr. Miller’s team also performed grip strength tests, and found that the neuroprosthesis enabled voluntary and intentional adjustments in force and grip strength – key factors in successfully performing everyday tasks naturally.
The multi-electrode array implant detects the activity of about 100 neurons in the brain, which is just a fraction of the millions of neurons involved in making the hand movements. However, Miller points out that the neurons they are detecting are output neurons normally responsible for sending 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,” Miller said.
Miller added that, while the temporary nerve block used in the study is a useful model of paralysis, it doesn’t replicate the chronic changes that occur after prolonged brain and spinal cord injuries. For this reason, the next test for the system will be in primates suffering long-term paralysis to study how the brain changes as it continues to use the device.
However, the ultimate aim for the team is for the system to restore movement in human paralysis sufferers. “This connection from brain to muscles might someday be used to help patients paralyzed due to spinal cord injury perform activities of daily living and achieve greater independence,” said Miller.
The results of the Northwestern University team’s study, which was funded by the National Institutes of Health (NIH), appears in the journal Nature.